What evidence supports the use of sunscreen (Sun Protection Factor) in reducing the risk of skin cancer?

From the Guidelines

Regular use of broad-spectrum sunscreen with SPF 30 or higher significantly reduces the risk of skin cancer, particularly squamous cell carcinoma. The evidence from studies such as 1 and 1 suggests that sunscreen use can prevent squamous cell skin cancer, although the evidence for melanoma prevention is mixed.

Key Points to Consider:

• Sunscreens that block both ultraviolet A (UV-A) and ultraviolet B (UV-B) light may be more effective in preventing squamous cell cancer and its precursors than those that block only UV-B light 1.
• Observational studies indicate that intermittent or intense sun exposure is a greater risk factor for melanoma than chronic exposure, and preventing sunburn, especially in childhood, may reduce the lifetime risk for melanoma 1.
• Clinical trials have demonstrated that sunscreens are effective in reducing the incidence of actinic keratoses, the precursors to squamous cell carcinoma 1.
• To be effective, sunscreens must be applied correctly, including applying sunscreen and allowing it to dry before going outdoors and getting any UV exposure, and reapplying sunscreen after leaving the water, sweating, or drying off with a towel 1.

Recommendations for Sunscreen Use:

• Apply 1 ounce (about a shot glass full) of sunscreen to all exposed skin 15-30 minutes before sun exposure and reapply every two hours, or immediately after swimming or excessive sweating.
• Use physical sunscreens containing zinc oxide or titanium dioxide for immediate protection by reflecting UV rays.
• Be aware of the active ingredients in sunscreens and try sunscreens with different ingredients if adverse effects are experienced. Overall, while the evidence for melanoma prevention is not as strong, the use of broad-spectrum sunscreen with SPF 30 or higher is still recommended as part of a comprehensive skin cancer prevention strategy, along with other measures such as avoiding direct exposure to midday sun, covering skin exposed to the sun, and seeking shade 1.

From the Research

Evidence for Sunscreen Reducing Skin Cancer Risk

• The use of sunscreen has been shown to reduce the risk of skin cancer, including melanoma and non-melanoma skin cancers 2, 3.
• Sunscreen use has been found to reduce the development of precancerous solar keratosis and the recurrence of squamous cell carcinomas 2.
• The incidence of melanoma and squamous-cell carcinoma is reduced with sunscreen use, although the effect of sunscreen on basal-cell carcinoma is relatively less pronounced 3.
• A systematic review and meta-analysis found that the overall meta-analysis did not show a significant association between skin cancer and sunscreen use, but the strength of the association between risk of skin cancer and sunscreen use has constantly decreased since the early 1980s 4.

Factors Affecting Sunscreen Efficacy

• The sun protection factor (SPF) is affected by application density, water resistance, and other factors 2.
• The correct use of sunscreens should be combined with the avoidance of midday sun and the wearing of protective clothing and glasses, as part of an overall sun protection regimen 2.
• The type of sunscreen and adherence to recommended guidelines are crucial in deriving the intended effect of sunscreen in reducing skin cancer risk 3.

Safety of Sunscreens

• Current evidence suggests that the likelihood of harm from the use of sunscreens containing nanoparticles is low, but further research into this area is required 5.
• Sunscreens have been proven to reduce rates of non-melanoma and melanoma skin cancers, and their use in prevention should be encouraged 5.
• The FDA regulates sunscreen products in the USA, and manufacturers are required to evaluate their products on SPF and broad-spectrum UVA protection 6.