Predictors of Sunburn among Canadian Adults

Preventive Medicine 33, 305–312 (2001) doi:10.1006/pmed.2001.0888, available online at http://www.idealibrary.com on

Predictors of Sunburn among Canadian Adults Mark P. Purdue, M.Sc.,*,1 Loraine D. Marrett, Ph.D.,* Larry Peters, Ph.D.,† Jason K. Rivers, M.D., FRCPC†,‡ *Division of Preventive Oncology, Cancer Care Ontario, 620 University Avenue, Suite 1500, Toronto, Ontario M5G 2L7; †Institute of Health Promotion Research, University of British Columbia, Vancouver, British Columbia; and ‡Division of Dermatology, British Columbia Cancer Agency, Vancouver, British Columbia, Canada Published online August 17, 2001

Background. Data from the 1996 National Survey on Sun Exposure & Protective Behaviors (4,023 respondents) were analyzed to identify independent predictors of sunburn among adult Canadians. Methods. Multivariate models predicting sunburn odds were developed using unconditional logistic regression. Backward elimination model selection was used to identify independent predictors of sunburn. Results. Nonbehavioral characteristics found to predict sunburn were younger age, male sex, light skin color, nonblack hair color, and birthplace in North America or Europe. Behavioral predictors of sunburn included high awareness of the UV Index, working outdoors in the summer, longer leisure time in the sun, forgetfulness about protecting oneself from the sun, and seeking a tan. Sun avoidance between 11 AM and 4 PM was associated with lower odds of sunburn, while seeking shade when outside and use of protective clothing showed nonsignificant associations with lower sunburn odds. Sunscreen use was found to have a nonsignificant positive association with sunburn. Conclusions. These findings highlight risk factors to be considered in the targeting of sunburn reduction strategies to high-risk groups and suggest that sun avoidance, seeking shade, and use of protective clothing may be effective in preventing sunburn. 䉷 2001 American Health Foundation and Academic Press

Primary funding for the 1996 Canadian National Survey on Sun Exposure & Protective Behaviors was obtained from a grant held by Dr. Chris Lovato, Dr. Jason Rivers, and Mr. Richard Gallagher from the National Cancer Institute of Canada, supported with funds from the Canadian Cancer Society (Grant 007066), the Canadian Dermatology Association, and Environment Canada. Other supporters included Health Canada, the Canadian Association of Optometrists, and BC Tel. Funding for the analyses reported in this article was provided by Health Canada (Contract 8-SC2028). 1 To whom reprint requests should be addressed. Fax: (416) 9717554. E-mail: [email protected].

Key Words: sunburn; risk factors; Canada; logistic models. INTRODUCTION

Melanoma and nonmelanocytic skin cancers, having risen substantially in incidence in fair-skinned populations over the past 2 decades [1], are important public health problems in Canada. It has been estimated that 3,700 new cases of malignant melanoma will have occurred in Canada in 2000, while the frequency of new cases of nonmelanocytic skin cancers (mostly squamous cell and basal cell carcinomas) for this time period is predicted to reach 68,000 [2]. There is strong evidence that sun exposure is a causal factor in the induction of skin cancer, although the more specific details of pathogenesis remain uncertain. One particular aspect of sun exposure that has been the focus of considerable research is sunburn—a biological marker of intense exposure of susceptible skin to ultraviolet (UV) radiation. Sunburn has been consistently found to be associated with the development of cutaneous melanoma [3], and there is also evidence of an association with squamous cell [4–6] and basal cell carcinomas [4, 7, 8]. The identification of behavioral and nonbehavioral predictors of sunburn would be helpful in the development of effective public health interventions. Although a considerable amount of published literature has reported risk factors associated with sunburn, only five of the reported studies sought to identify in a multivariate context independent predictors of sunburn among children [9–11] or adults [12, 13]. The National Survey on Sun Exposure & Protective Behaviors (NSSE&PB) was conducted in 1996 to provide information about sun exposure and protective behaviors in the Canadian population [14]. The data from this survey were analyzed using multivariate modeling to identify independent risk factors for sunburn in the

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0091-7435/01 $35.00 Copyright 䉷 2001 by American Health Foundation and Academic Press All rights of reproduction in any form reserved.

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adult (age 15 years or older) Canadian population as well as to estimate the predictive effects of these risk factors using odds ratios. Sunburn was defined in the survey as “. . . any reddening of the skin received either from the sun or artificial methods of tanning” [14]. A future report will present similar analyses for children. METHODS

Data Set Responses from all participants in the 1996 NSSE& PB were used for the purposes of these analyses. The methodology of this survey is briefly described in this article; a more detailed description has been previously reported [15]. The survey was carried out by Statistics Canada using trained telephone interviewers during the month of September 1996. Respondents were asked to report on their sun exposure and protective behaviors for the period June through August 1996. The target population included all persons age 15 years or older residing in Canada, with the exception of residents of institutions (hospitals, care facilities, and correctional facilities), residents of Yukon and Northwest Territories, and residents of households without telephones. A sample of this population was drawn using random-digit dialing. When a household was reached, an attempt was made to list all eligible household residents and to sample one of these residents at random. Data collection was carried out using computer-assisted telephone interviewing technology. All interviews were carried out with the selected respondent only. The response rate was 69%, with 4,023 respondents. Ethics approval to conduct this survey was received from the University of British Columbia Behavioural Research Ethics Board. Analysis Statistical analysis of the national survey data was performed using SAS statistical software [16]. Sample weights have been calculated by Statistics Canada based upon a number of factors (probability of selection, nonresponse adjustments, and adjustments for region, age, and sex) in order to permit population estimates. As a means of accounting for the sample design, the sample weights were used in all analyses and the effective sample size was downweighted by the overall calculated design effect (deff ⫽ 1.27). In accordance with Statistics Canada guidelines [14], the reliability of all weighted population estimates reported in this paper were screened on the basis of the coefficient of variance (CV) as follows: if the CV is less than 16.5%, the data are shown without qualification; if the CV is between 16.5 and 33.3%, the data are released with qualification; if the CV is greater than 33.3% (or sample size on

which the estimate is based is less than 30), the data are suppressed. Potential sunburn predictors consisted of the following: age group (15–24, 25–34, 35–44, 45–64, 65⫹), sex (female, male), region of Canada (Ontario, Quebec, Atlantic provinces, Prairie provinces, British Columbia), income adequacy (see below), birthplace (see below), skin color (light, medium, dark), hair color (black, dark brown, light brown, blond, red), personal history of skin cancer (yes, no), family history of skin cancer (yes, no), awareness of the UV Index (always/often, sometimes/ rarely/never), worked outdoors over the previous summer (yes, no), time spent in the sun during 1996 winter travel to a sunny place (never traveled; traveled, ⱕ2 h/ day in sun; traveled, ⬎2 h/day in sun), and leisure time sun exposure (see below). Income adequacy is a derived variable that combines household size and household income to categorize respondents by income level (lowest, lower middle, upper middle, highest). Birthplace had been collapsed into seven categories (Canada, United States, United Kingdom, Other Europe, Asia, Caribbean/South America) in the public use data set to ensure respondent confidentiality. In the interest of minimizing the number of estimated model parameters, birthplace categories with similar associations with sunburn were further collapsed to form three categories (North America, Europe, Other). All of these variables were treated as categorical for the purposes of modeling. Given that sun protection information was collected only from respondents with at least 30 min per day (min/day) of leisure time in the sun, a 25-category composite variable, “leisure time sun exposure,” was created in the interest of maintaining a universe that represented the entire Canadian population ages 15 years and older. This composite variable combined leisure time in the sun (reported as ⬍30 min/day, 30–59 min/ day, 60–119 min/day, or 120⫹ min/day) and three variables summarizing the respondents’ practice of sun protection behaviors: “sun avoidance” (always or often avoided the sun between 11 AM and 4 PM and always or often sought shade), “hat/clothing” (always or often wore protective clothing and always or often wore a hat), and sunscreen use (always or often used sunscreen on the face/body). For this overall measure of sun exposure, eight separate categories of behavior were created within each level of leisure time in the sun of 30 min/ day or greater (no protection, sun avoidance only, hat/ clothing only, sunscreen only, sun avoidance and hat/ clothing, sun avoidance and sunscreen, hat/clothing and sunscreen, all three behaviors). The resulting leisure time sun exposure consists of 25 categories: the referent category of less than 30 min/day leisure time in the sun and 24 leisure time/behavior categories.

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The crude association between sunburn (0 vs 1⫹ sunburns over previous summer) and each potential predictor was estimated using odds ratios (OR) calculated from cross-tabulations. Those variables found to be significantly associated with sunburn (P ⬍ 0.10 using Pearson ␹2 statistic) were included in the multivariate analysis. A multivariate model of sunburn odds among adult Canadians was developed using unconditional logistic regression. Modeling was performed using the SAS procedure LOGISTIC [16]. All variables found to be crudely associated with sunburn (as defined above) were combined with sex, age, skin color, and region of Canada into one model. Backward elimination using the likelihood ratio test (significance level of 0.05 or less for staying in the model) was performed to identify the model with the greatest explanatory value. Region of Canada was forced into the final model, given that sampling was stratified according to geographic region. Odds ratios with accompanying 95% confidence intervals (CIs) were calculated to describe the association with sunburn of each predictor variable retained in the final model. In order to examine whether the effect of leisure time in the sun increases monotonically, the 25level leisure-time sun exposure variable was replaced by leisure time in the sun (⬍30 min/day, 30–59 min/ day, 60–119 min/day, or 120⫹ min/day) in the final model; a test for trend was performed using the Wald test by modeling the variable as a single quantitative covariate. The modeling process was repeated to develop a multivariate model of sunburn odds among the subset of adult Canadians who spent 30 min/day or more leisure time in the sun. The same potential predictors were included in this analysis, with the exception that leisure time in the sun and specific sun-protective behaviors (avoiding the sun between 11 AM and 4 PM, seeking shade when outside, wearing protective clothing, wearing a hat, using sunscreen) were assessed independently. In addition, the following possible barriers to sun protection were considered potential predictors: finding sun protection inconvenient, being unconcerned about sun protection, sometimes forgetting to protect oneself from the sun, wanting to get a suntan, and other reasons for not protecting oneself. In light of previous findings suggesting that the risk of sun-related events such as nevi and skin cancers associated with sun behaviors may be modified by inherent skin sensitivity to the sun [7, 17, 18], we assessed the possible presence of statistical interaction between skin color (treated as an ordinal variable for the purposes of testing for interaction) and sun behaviors (i.e., leisure time in the sun, sun-protection behaviors, having sought a tan, and having worked outdoors). Interaction was assessed by individually adding product terms of these variables to the final main-effects model. The

likelihood ratio test was used to determine whether the presence of each interaction term significantly (P ⬍ 0.05) improved the fit of the model. RESULTS

Approximately 53% of Canadians age 15 years or older experienced one or more sunburns during the summer, ranging from 68% of those ages 15–24 to less than 21% of those ages 65 and over. A higher proportion of males reported sunburn than females (57% vs 50%). All factors were found to have strong (P ⬍ 0.10) crude associations with sunburn with the exception of time spent in the sun during winter travel to sunny places. Higher odds of sunburn were found for the following characteristics: residence in Ontario (vs Quebec residence), younger age, male sex, upper middle to highest income adequacy, birthplace in North America, lighter skin color, lighter hair color, no personal history of skin cancer, family history of skin cancer, high awareness of the UV Index, having worked outdoors over the previous summer, and increasing leisure-time sun exposure. The distributions and crude odds ratios for all predictors except leisure-time sun exposure are presented in Table 1. Although income adequacy showed a crude association with sunburn, it was not included in further analyses due to its high level of missing data (13% of all records). Complete information on all remaining crude predictors was present for 3,423 observations (85.1% of all records). Variables describing personal history of skin cancer and family history of skin cancer were removed from the model without a significant loss of explanatory value. Odds ratios with accompanying 95% CIs describing the association with sunburn of the independent variables from the final model except leisuretime sun exposure are provided in Table 1. Residence in Quebec was accompanied by a slightly lower odds of sunburn than Ontario residence; no other Canadian regions of residence were found to differ from Ontario with respect to sunburns. Increasing age was accompanied by a decrease in sunburn odds, while males had about a 30% higher odds of sunburn than females. Those born in Europe were found to have a slightly lower but nonsignificant odds of sunburn in comparison with those born in North America. However, a strong inverse association was observed for having been born in other parts of the world compared with North American-born. Higher odds of sunburn were observed for those reporting medium or light skin color (vs dark skin) as well as for those with dark brown, light brown, blond, or red hair (compared with black hair). Modest increases in sunburn odds were observed for indicating high awareness of the UV Index and for having worked outdoors over the previous summer.

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TABLE 1 Predictors of Sunburn: Constitutional and Behavioral Factors Other Than Leisure-Time Sun Exposure, NSSE&PB 1996 (Universe: All Canadian Residents Ages 15⫹ Years) No sunburn Variable Region of Canada

Age (years)

Sex Birthplaced

Hair colore

Skin colorf

Awareness of UV Indexg Worked outdoors over previous summerh Personal history of skin canceri Family history of skin cancerk Income adequacy l

Categories Ontario Quebec Atlantic provinces Prairie provinces British Columbia 15–24 25–44 45–64 65⫹ Female Male North America Europe Other Black Dark brown Light brown Blond Red Dark Medium Light Sometimes/rarely/never Always/often No Yes No Yes No Yes Lowest–middle Upper middle–highest

Sample

Pop. %

500 519 255 341 300 190 658 596 471 1,093 822 1,551 172 190 322 713 540 259 76 289 906 717 940 945 1,657 257 1,805 105 1,723 173 851 758

45.0 51.9 44.8 44.3 46.5 32.2 35.1 56.7 79.0 50.5 43.0 43.7 55.0 71.7 65.4 46.8 43.0 39.5 41.4 61.3 46.8 42.6 50.1 43.5 49.9 33.6 46.1 62.3 47.8 37.9 49.3 41.7

1⫹ sunburns c

Sample

Pop. %c

ORcrudea

587 474 297 409 341 384 1,183 429 112 1,027 1,081 1,896 130 82 182 765 704 369 88 180 996 931 931 1,171 1,611 497 2,047 59 1,843 246 853 1,041

55.0 48.1 55.3 55.7 53.5 67.8 64.9 43.4 21.0 49.5 57.0 56.3 45.0 28.3 34.6 53.2 57.0 60.5 58.6 38.7 53.2 57.4 50.0 56.6 50.1 66.4 53.9 37.7 52.2 62.1 50.7 58.3

1.00 0.76 1.01 1.03 0.94 1.00 0.88 0.36 0.13 1.00 1.35 1.00 0.64 0.31 1.00 2.15 2.50 2.90 2.67 1.00 1.80 2.13 1.00 1.30 1.00 1.97 1.00 0.52 1.00 1.51 1.00 1.36

ORadjb (95% CI) 1.00 0.76 0.89 0.81 0.90 1.00 1.03 0.46 0.16 1.00 1.33 1.00 0.77 0.36 1.00 1.61 1.72 1.65 2.21 1.00 2.00 2.75 1.00 1.24 1.00 1.55 —j —j —j —j —j —j

(0.60–0.97) (0.64–1.25) (0.62–1.06) (0.68–1.20) (0.80–1.33) (0.35–0.60) (0.11–0.22) (1.09–1.60) (0.56–1.05) (0.25–0.51) (1.19–2.18) (1.25–2.37) (1.14–2.39) (1.29–3.81) (1.50–2.66) (2.00–3.77) (1.04–1.49) (1.23–1.95)

Note. %, percentage; OR, odds ratio; CI, confidence interval. a Unadjusted odds ratio. b Odds ratio adjusted for all other variables in the model (including leisure-time sun exposure). c Population percentages obtained using sample weights. Percentages may not sum to 100.0% due to rounding off to the first decimal. d Frequency missing: 2. e Frequency missing: 5. f Frequency missing: 4. g Frequency missing: 36. h Frequency missing: 1. i Frequency missing: 7. j Variable not retained in final model. k Frequency missing: 38. l Frequency missing: 520.

The 25-level leisure-time sun exposure variable enabled investigation of the effects of sun-protection behaviors and duration of leisure time spent in the sun on sunburn risk among all respondents; odds ratios with 95% CIs adjusted for other covariates of the final model are presented in Table 2. Odds ratio estimates suggest that, conditional on time in the sun, the “sun avoidance” and “hat/clothing” summary behaviors have lower odds of sunburn com-

pared with no protective behavior. In order to more directly assess the effects of sun-protection behaviors, the odds ratios were recalculated using the “no protection” categories within each level of leisure time in the sun as the referent categories. Within each level of leisure time, the reporting of only “sun avoidance” behavior had lower odds of sunburn than reporting no protective behaviors [OR (95% CI) of 0.52 (0.28–0.97), 0.49 (0.30–0.80), and 0.81 (0.39–1.65) for 30–59, 60–119,

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TABLE 2 Predictors of Sunburn: Leisure-Time Sun Exposure, NSSE&PB 1996 (Universe: All Canadian Residents Ages 15⫹ Years) Leisure time in sun (min/day) ⬍30

30–59

a

Protective behavior

OR (95% CI)

N/A All three behaviors Hat/clothingb ⫹ sun avoidancec Sun avoidance ⫹ sunscreend Hat/clothing ⫹ sunscreen Sun avoidance only Hat/clothing only Sunscreen only None

1.00 — — — — — — — —

a

OR (95% CI) 1.90 1.03 2.82 3.05 1.38 1.83 3.86 2.65

— (0.79–4.56) (0.47–2.24) (1.39–5.71) (0.94–9.95) (0.78–2.45) (0.97–3.45) (2.20–6.77) (1.85–3.79)

60–119 a

OR (95% CI) 1.84 1.74 1.79 2.31 1.44 2.08 3.24 2.95

— (0.84–4.03) (0.97–3.12) (0.91–3.53) (1.14–4.69) (0.89–2.33) (1.27–3.41) (2.10–5.01) (2.18–3.99)

120⫹ a

OR (95% CI) 1.02 1.78 1.45 2.35 3.70 2.89 5.21 4.58

— (0.36–2.86) (0.87–3.65) (0.61–3.43) (1.10–5.01) (1.84–7.41) (1.77–4.73) (3.23–8.41) (3.29–6.39)

Note. OR, odds ratio; CI, confidence interval. a Odds ratio adjusted for region of Canada, age, sex, birthplace, hair color, skin color, awareness of UV Index, worked outdoors over previous summer. b “Hat/clothing” behavior is defined as always or often wearing protective clothing and wearing a hat when outside in leisure time. c “Sun avoidance” behavior is defined as always or often avoiding the sun between 11 AM and 4 PM and seeking shade when outside in leisure time. d “Sunscreen” behavior is defined as always or often applying sunscreen to the face and body when outside in leisure time.

and 120⫹ min/day in the sun, respectively]. Similarly, reporting of only “hat/clothing” behavior had consistently lower sunburn odds than reporting no protection [OR (95% CI) of 0.69 (0.36–1.35), 0.71 (0.43–1.17), and 0.63 (0.38–1.05) for 30–59, 60–119, and 120⫹ min/day in the sun, respectively]. Unlike with the other behaviors, the reporting of sunscreen use only had consistently higher odds of sunburn than reporting no protection [OR (95% CI) of 1.46 (0.80–2.67), 1.10 (0.7–1.73), and 1.14 (0.68–1.89) for 30–59, 60–119, and 120⫹ min/ day in the sun, respectively]. The odds ratios for categories involving combinations of behaviors are generally consistent with the idea that sun avoidance and hat/ clothing behaviors are accompanied by lower sunburn odds than no protection, while sunscreen use is associated with higher sunburn odds. The effects observed for the different levels of leisuretime sun exposure suggest that leisure time spent in the sun of 30 min/day or longer is associated with an increase in sunburn odds (with ⬍30 min/day as a baseline) regardless of protection practices. However, it is unclear from this model whether there is a monotonic increase in the odds of sunburn with increasing leisure time in the sun, conditional on level of protection. As a means of addressing this question, another model of sunburn odds was fit containing leisure time in the sun (defined using indicator variables) and adjusting for region of Canada, age, sex, hair color, skin color, awareness of UV Index, and worked outdoors over the previous summer. The effects estimated from the fit of this model suggest a monotonic increase in sunburn odds with increasing leisure time in the sun [test for trend: ␹ 2 ⫽ 80.3, 1 df (P ⬍ 0.0001)]; however, it must be

pointed out that this model does not adjust for the effects of protective behaviors. Unlike with the analysis of all Canadian adults, the multivariate model of sunburn fit for the subset of Canadian adults who reported spending 30 min/day or more in the sun during leisure time was able to adjust for leisure time in the sun and specific sun-protection behaviors separately and to adjust for potential barriers to sun protection (Table 3). Complete information on the study factors of interest was present for 2,972 observations (94.0% of those with 30⫹ min/day of sun). The associations with sunburn of all the variables measuring factors other than leisure time in the sun and protective behaviors (age, sex, region of Canada, birthplace, skin color, hair color, awareness of UV Index, worked outdoors over the previous summer) were virtually identical to those from the previous model, with the exception that residence in Quebec was no longer significantly associated with sunburn (data not shown). The odds of sunburn for 60–119 min/day leisure time in the sun were not significantly different from those for 30–59 min/day in the sun. However, leisure time in the sun of 2 h or more had significantly higher odds of sunburn (OR 1.49; 95% CI 1.15–1.92). Always or often avoiding the sun between 11 AM and 4 PM was associated with a statistically significant 24% decrease in sunburn odds (OR 0.76; 95% CI 0.61–0.95) in comparison with sometimes/rarely/never performing the behavior, while smaller nonsignificant decreases in sunburn odds were found for always or often seeking shade or wearing protective clothing. No difference in sunburn odds was found for always or often wearing a hat, while

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TABLE 3 Predictors of Sunburn: Leisure-Time in the Sun, Protective Behaviors, and Barriers to Sun Protection, NSSE&PB 1996 (Universe: All Canadian Residents Ages 15⫹ Years with 30⫹ Min/Day Leisure Time in Sun) Variable Leisure time in the sun

Avoid the sun between 11 AM and 4 PM Seek shade when outdoors Wear protective clothing Wear a hat Always/often use sunscreen on face and body Sometimes forgot to protect oneself from the sun Wanted a tan

Category 30–59 min/day 60–119 min/day 120⫹ min/day Sometimes/rarely/never Always/often Sometimes/rarely/never Always/often Sometimes/rarely/never Always/often Sometimes/rarely/never Always/often No Yes No Yes No Yes

ORa 1.00 1.06 1.49 1.00 0.76 1.00 0.82 1.00 0.86 1.00 0.92 1.00 1.21 1.00 2.35 1.00 1.52

95% CI 0.84–1.35 1.15–1.92 0.61–0.95 0.66–1.01 0.70–1.05 0.75–1.12 0.97–1.51 1.94–2.86 1.23–1.87

Note. OR, odds ratio; CI, confidence interval. a Odds ratio adjusted for region of Canada, age, sex, birthplace, hair color, skin color, awareness of UV Index, worked outdoors over previous summer.

sunscreen use was associated with a slight nonsignificant increase in the odds of sunburn (OR 1.21; 95% CI 0.97–1.51). Two of the five possible barriers to protection that were included in the analysis were found to be significantly associated with sunburn. Individuals who sometimes forgot to protect themselves from the sun were found to have more than twice the odds of sunburn compared with those who were not forgetful about sun protection (OR 2.35; 95% CI 1.94–2.86). A modest positive association was observed between wanting to get a suntan and sunburn (OR 1.52; 95% CI 1.23–1.87). No evidence of interaction was found between skin color and leisure time in the sun or any of the protective behaviors or barriers to protection. DISCUSSION

Sunburn is an inflammatory reaction of the skin to unprotected and/or excessive skin exposure to UV radiation, ranging from reddening to severe blistering. In addition to causing sunburn, excessive UV exposure also causes cellular DNA damage in the epidermis leading to gene mutation and the induction of skin cancer [19]. Sunburn is considered to be an indicator of “intermittent”-type sun exposure [3]—that is, intense periodic sun exposure of unprotected skin. There is evidence that the higher the proportion of cumulative sun exposure that is received as “intermittent,” the greater the risk of melanoma [20] and basal cell carcinoma [4, 7, 8], the most fatal and most common forms of skin cancer, respectively. There has therefore been considerable emphasis on encouraging behaviors that reduce the risk

of sunburn. In order to do this effectively, it is useful to know who gets sunburn and under what circumstances. The present analysis examined the relationships between reported sunburn among Canadian adults and two types of variables: characteristics of the individual (e.g., sex, age, skin color, etc.), which identify those individuals most at risk of sunburn, and behaviors (e.g., time in the sun, use of and barriers to protective behaviors) related to the production of sunburn. The survey found sunburn to be very common among Canadian adults, with approximately half of respondents reporting one or more burns. The individual characteristics that were found to be related to increased risk of sunburn among adults were young age, male gender, light skin color, hair color other than black (particularly red hair), and birthplace in North America. In terms of behaviors, those who spent more leisure time in the sun, who were very aware of the UV Index, who worked outdoors, who sometimes forgot to protect themselves from the sun, and who sought a tan were more likely to be sunburned. Individuals who avoided the sun during peak UV hours were significantly less likely to report sunburn. Nonsignificant decreases in sunburn odds were found for seeking shade and wearing protective clothing, while sunscreen use was found to have a nonsignificant positive association with sunburn. There are obviously different reasons why these factors predict sunburn. Younger adults, men, and those who work outdoors are likely to experience more sunburn because of excess exposure that is not captured in the behavior variables, while those with fair coloring

PREDICTORS OF SUNBURN

lack protective pigmentation. Although the directions of the observed associations with sunburn for increased leisure time in the sun (positive association) and for avoiding the sun between 11 AM and 4 PM, seeking shade, and wearing protective clothing (negative associations) were as one would predict, the magnitude of these associations were fairly weak. This may be at least partly due to the effects of measurement error in assessing sun behaviors, given that self-reports of purported usual behavior over a summer were collected rather than direct measurements of actual behaviors on specific days when sunburn did or did not occur. The apparent lack of protection from sunburn associated with sunscreen use is of interest in light of studies reporting an increased risk of melanoma or nevi with use of sunscreen [21–23]. The latter findings have been interpreted as supporting an indirect causal role for older sunscreens, in particular, through their lack of effectiveness against the UVA portion of the spectrum [22]. Data from the NSSE&PB suggest that sunscreens are also not effective at preventing sunburn, which is caused by the UVB rays that sunscreens are specifically designed to block. In fact, a nonsignificant positive association was observed between sunscreen use and sunburn odds. One possible explanation for this finding is that sunscreens are not being applied properly, such that people increase their time in the sun under the mistaken assumption that they are adequately protected by the improperly applied sunscreen. Indeed, there is evidence that people typically apply sunscreen after the onset of sun exposure (e.g., after arrival at the beach) [24] and in insufficient amounts [24–26]. It is also possible that this association reflects the inability to adequately control for the confounding effects of skin sensitivity to the sun, given that people who burn easily appear to be most likely to use sunscreen [27]. Of course, one must be careful in interpreting associations between behaviors and outcomes in cross-sectional data such as these. The independent predictors of sunburn among adults identified in this analysis are consistent with those previously reported in the literature. Using data from a telephone survey of adults in Melbourne, Australia, Hill and colleagues [12] also found sensitive skin type, young age, and male sex to be independently associated with increased risk of sunburn. A “body exposure index” created taking into account information on time in the sun and hat, clothing, and sunscreen coverage showed an independent association between increasing sun exposure and increased sunburn risk. Similarly, Melia and Bulman [13] identified young age, male sex, sunsensitive skin, and tan-seeking behavior as independent predictors of sunburn among a sample of British adults. Neither study considered in their respective analyses any of the additional predictors identified from the NSSE&PB data.

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Data from the 1996 NSSE&PB provide the first opportunity to examine sun-related behaviors in a large sample of Canadians across the entire country. As such, they represent a baseline for monitoring future sun behavior and outcomes. Unfortunately, there are no previous national data on this subject. It is therefore not possible to determine whether the apparent leveling off of the incidence of melanoma in Canada after decades of steady increase [1] is related to changing sun exposure or protection behaviors. Nevertheless, internal analysis of the NSSE&PB data is useful for assessing the interrelationships between behaviors and outcomes such as sunburn, which is in itself a predictor of skin cancer risk. Knowledge regarding who gets sunburn and under what circumstances would be useful in the development of programs to encourage behaviors that reduce the risk of skin cancer. Previous descriptive analysis of the Ontario portion of the NSSE&PB has noted the circumstances of sunburn [28]. That analysis showed that the most common activity engaged in when Ontario adults received their worst sunburn was participation in or watching of outdoor recreation activities (47%), with outdoor work (32%) the second most commonly cited activity. Women were more likely than men to report engaging in outdoor recreation when receiving their worst sunburn (52% vs 43%), while men were more likely to have received their worst burn while working outdoors (42% vs 21%). The interpretation of these findings is restricted by two limitations to the analysis. First, firm inferences in relation to temporality of events cannot be made based on cross-sectional data. This means, for example, that one cannot conclude that frequent use of sunscreens or high awareness of the UV Index increases the risk of getting sunburned; equally well, one could conclude that those who experience sunburn are more likely to use sunscreens or check the strength of UV radiation when going outside in future. A further limitation of this analysis is that it was not possible to properly account for the survey design effect in calculating the variance surrounding estimated odds ratios, due to the suppression of sample design information for reasons of confidentiality. The only available technique of accounting for the survey design in calculating variance was to downweight observations by the design effect so as to reflect the effective sample size. Given that such adjustments of the effective sample size often result in a conservative estimate of variance surrounding regression coefficients [29], it may be considered unlikely that the factors found to be significant predictors of sunburn from this analysis would not have been so identified using ideal analytic techniques. However, with this method one cannot guarantee that the true sample variance has been estimated for any given odds ratio, given that design effects can vary not only in magnitude but also in direction across different sample

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