How to apply sunscreen for maximum protection

Cancerous Skin Growths

How to apply sunscreen for maximum protection

Published: September, 2005

Most families follow common medical advice and take along a bottle of sunscreen when they're spending a day in the sun. But how do you know if you're applying enough? Most people don't, but a letter published in the June 22, 2002, issue of the British Medical Journal may help clarify the amount of sunscreen you should use and how often you should apply it.

The letter, written by Drs. Steve Taylor and Brian Diffey, suggests people follow the "rule of nines" to get the sun protection factor (SPF) that's listed on the bottle. According to the rule, you should divide your body into 11 different sections, each making up about 9% of your total surface area:

  • Head, neck, and face
  • Left arm
  • Right arm
  • Upper back
  • Lower back
  • Upper front torso
  • Lower front torso
  • Left upper leg and thigh
  • Right upper leg and thigh
  • Left lower leg and foot
  • Right lower leg and foot

For sufficient protection, use a two-finger approach: cover each of the 11 sections with enough sunscreen to span the length of your pointer and middle fingers.

The authors admit that this is more sunscreen than most people feel comfortable wearing, so they suggest that people put on half that amount at one time, and then apply another dose a half hour later. Studies have shown that sunscreen users do not apply enough sunscreen to protect the whole body. As a result, the actual SPF is close to half that on the product label.

It's also worth noting that according to the American Academy of Dermatologists, staying out of the sun is the best way to prevent skin cancer. Because harmful sun rays like UVA and infrared get through sunscreen, you shouldn't think of it as a shield against the sun or use it as an excuse to stay out longer. Although sunscreen is an important part of sun protection, it is second to wearing a shirt and hat and avoiding sun exposure altogether (especially between the hours of 10 a.m. and 4 p.m.).

August 2002 Update

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Artificial Tanning and Carcinoma Risk

Artificial tanning devices such as sunlamps are gaining popularity — especially among young adults and women — in spite of the fact that their use is linked to skin cancer. The UV radiation emitted from these devices, along with the sunburns they elicit, are risk factors for two of the most common types of skin cancer: basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). Though the link between carcinomas and artificial tanning devices is generally accepted, there are few data connecting the two. So investigators in New Hampshire studied the risk of BCC and SCC associated with such methods. The results were published in the February 6, 2002, issue of the Journal of the National Cancer Institute.

Subjects were BCC and SCC patients, ages 25–74. They answered questions on their sun sensitivity, sun exposure, and artificial tanning methods, if any. Those who had either used a sunlamp or tanning bed, or gone to a tanning salon also gave their ages at first and last use.

Participants who used tanning devices were 2.5 times more likely to develop SCC and 1.5 times more likely to develop BCC than those who did not use the devices. Even after participants' past sunburns and sun exposure were taken into account, the excess risk for SCC and BCC associated with artificial tanning devices was still present. What's more, for every ten years earlier that a person started artificial tanning, the risk of BCC and SCC increased by 20% and 10%, respectively.

The study supports earlier suggestions that tanning device use may be contributing to the increasing incidence of BCC and SCC. Future research will hopefully help assess the link between frequency of tanning lamp use and carcinoma risk, an issue that was not addressed in this study.

May 2002 Update

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