Sun protection and shade use

This cohort study established urinary thymine dimers (T=T) as a validated biomarker of UVR exposure, the primary environmental cause of basal cell carcinoma. Creatinine-corrected urinary T=T showed significant correlation with T=T levels in skin tissue (p < 0.05). Single outdoor exposures demonstrated a significant dose-response relationship in both adults and children, with equivalent T=T formation per unit dose regardless of age. Among outdoor workers with continuous exposure, a mixed statistical model revealed steady-state T=T levels reflecting the preceding three days of UVR exposure. The study explicitly identifies that dose-limiting factors including clothing and sunscreen reduce biologically effective UV exposure, and concludes that the biomarker can assist in primary prevention of human skin cancer.

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In a matched case-control study of 100 BCC patients and 100 controls in Montenegro (2002-2003), fair skin was significantly associated with BCC development (t = 2.37, df = 99, p = 0.020). Skin that remained light after sun exposure showed a 3.14-fold increased risk of BCC (OR = 3.14, p = 0.001, 95% CI 1.59-6.18). Lighter hair color (t = 4.63, df = 99, p < 0.001) and lighter eye color (t = 2.86, df = 99, p = 0.005) were also significantly associated with BCC development, indicating that individuals with these UV-sensitive constitutional features face elevated risk.

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In a prospective cohort of 202 basal cell carcinoma patients with 253 lesions at Hospital Jaraguá, São Paulo, 77% reported exposure to ultraviolet radiation in both recreational and occupational forms. UV exposure was identified as a statistically significant factor in BCC development. The population showed 95.5% prevalence of phototypes I and II (fair skin), and 71.2% of tumors occurred on the face, the most sun-exposed body area. Actinic keratosis, a UV-induced precancerous condition, was present in 43.6% of patients. Incidence was 36 cases per 100,000 patients per year, with peak occurrence between ages 60-80 years (69% of cases, mean age 64 years), suggesting cumulative UV damage over decades as a primary driver.

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A case-control study of 100 histopathologically confirmed basal cell carcinoma cases matched with 100 controls by sex and age in the Montenegrin population identified sun radiation as a major risk factor. Individuals who always burned without tanning had significantly elevated risk (OR = 1.75; 95% CI = 1.20–2.55; p = 0.003). Those developing sunburns after two hours of exposure showed even greater risk (OR = 3.72; 95% CI = 2.39–5.79; p < 0.001). Persons who retained only light tan or no change after repeated childhood sun exposure had increased risk (OR = 2.92; 95% CI = 1.89–4.52; p < 0.001).

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