Preventing Skin Cancer

Sun Avoidance

Avoiding sunshine can help prevent most types of skin cancer.

  • Avoid sun exposure as much as possible between the hours of 10AM and 4PM
  • Don't stay in the sun for prolonged periods of time, even if you are wearing sunscreen
  • Seek shade
  • Avoid tanning beds
  • Even on cloudy days, 80% of sun’s UV rays reach you

You do not have to avoid the sun altogether. Learn how to protect your skin from the sun's harmful rays and practice "sun protection" and "sun safety" whenever you can. Cover up with sunscreen and protective clothing and be sensible about how much time you spend in the sun. These steps can help greatly reduce your risk of developing skin cancer.


Sunblock protects your skin by absorbing and/or reflecting UVA and UVB radiation. All sunblocks have a Sun Protection Factor (SPF) rating. The SPF rating indicates how long a sunscreen remains effective on the skin. A user can determine how long their sunblock will be effective by multiplying the SPF factor by the length of time it takes for him or her to suffer a burn without sunscreen.

For instance, if you normally develop a sunburn in 10 minutes without wearing a sunscreen, a sunscreen with an SPF of 15 will protect you for 150 minutes (10 minutes multiplied by the SPF of 15). Although sunscreen use helps minimize sun damage, no sunscreen completely blocks all wavelengths of UV light. Wearing sun protective clothing and avoiding sun exposure from 10 a.m. to 3 p.m. will also help protect your skin from overexposure and minimize sun damage.

The American Association of Dermatology (AAD) recommends that a "broad spectrum" sunblock with an SPF of at least 15 that is applied daily to all sun exposed areas, then reapplied every two hours. However, in some recent clinical trials, sunblocks with SPF 30 provided significantly better protection than sunblocks with SPF15. Therefore at UCSF, we recommend sunblocks with SPF of at least 30 with frequent reapplication.

Use broad spectrum sunscreen daily with SPF of 30 or greater- UVA/UVB protection. 

  • Apply ~30 minutes prior to sun-exposure.
  • Apply to all sun-exposed areas. Don't forget lips, ears, back of neck, or back of legs.
  • Apply a sufficient coat of sunscreen- most common mistake is being too stingy
  • Reapply every 2 hours when out in the sun- more frequently if in water or sweating
  • Use lip balm with sun block daily that is frequently reapplied
  • Chemical sunblocks- these function by absorbing the harmful energy of sunlight before it reaches your skin
    • Most chemicals used in sunblock only provide protection over a narrow range of UV radiation. Therefore, sunblocks often use combinations of chemical blockers to provide broad spectrum protection.
    • USCF typically recommends chemical sunblocks that contain Parsol 1789 (avobenzone) because of its superior protection against UVA radiation
    • Mexoryl (Anthelios) is another chemical sunblock that provides excellent broad spectrum UVA and UVB protection. It is not approved for use in the United States by the Federal Drug Administration (FDA) but is sold in Europe and Canada, often through internet sites.
  • Physical blockers- contain ingredients that scatter UV radiation before it reaches your skin
    • Titanium dioxide and zinc oxide are the only two physical sunblocks are generally considered equally effective
      both offer broad spectrum UVA and UVB protection
      good for sensitive skin

Sun Protective Clothing

Clothing is a simple and effective sun protection tool. It provides a physical block that doesn't wash or wear off and can shade the skin from both UVA and UVB rays. Long-sleeved shirts and pants, hats with broad brims and sunglasses are all effective forms of sun protective clothing.

The American Society for Testing and Materials has recently developed standards for manufacture and labeling of sun protective products. The new units for UV protection are called UPF (Ultraviolet Protection Factor). UPF measures the ability of the fabric to block UV from passing through it and reaching the skin.

  • Good UV Protection (for UPF 15-24),
  • Very Good UV protection (for UPF 25-39), or
  • Excellent UV Protection (for UPF 40-50)

Not all fabrics block UV light to the same extent. The Ultraviolet protective factor (UPF) of clothing depends on several factors including weave and chemical additives when manufactured, (such as UV absorbers or UV diffusers).

UPF factors in order of importance:

  • Weave: tightly woven fabric provides greater protection than loosely woven clothing. If you can see light through a fabric, UV rays can get through, too.
  • Color: Dark colors provide more protection than light colors by preventing more UV rays from reaching your skin.
  • Weight: also called mass or cover factor - heavier is better
  • Stretch: Clothing with less stretch generally has better UV protection
  • Wetness: Dry fabric is generally more protective than wet fabric.

The ideal sun-protective fabrics are lightweight, comfortable, and protect against exposure even when wet. Currently, only a few companies in the U.S. manufacture clothing that is specifically designed to be UV-protective. Their products include outerwear, pants, shirts, and hats for all sizes and shapes including children. See the sidebar at the left for recommended websites.

For those who enjoy water sports, consider using UV protective swimwear including rash guards and swimsuits. Some companies even sell UV protective flotation devices and swim diapers.

Additionally, you may use sunprotective clothing additives such as Sunguard Detergent. Sunguard detergent is an UV blocking additive that can be added to your laundry to transform everyday clothing into sun protective gear with a SPF 30. The active ingredient is Tinosorb™ FD, a UV protectant that can boost the SPF protection of a white cotton T-shirt from SPF 5 to UPF 30.

Examples of UV protective clothing (Pictures courtesy of SunPrecautions Clothing)