Suncreen: Know your numbers

There are several different types of ultraviolet radiation. Two kinds are associated with health risks: ultraviolet-A (UVA) and ultraviolet-B (UVB). UVA has been linked to skin aging (wrinkling) and skin cancer. UVB has been known to cause sunburn, skin aging and skin cancer. Since ultraviolet radiation can be neither seen nor felt, people are usually not aware of sun damage until long after exposure, and when the signs of sun damage manifest themselves. UVA and UVB can be at high levels regardless of the temperature or weather. This means that sunburns and skin aging can occur even on cool, cloudy days. Experts think that there are peak ultraviolet radiation levels between the hours of 10 am and 4 pm each day.

When skin is exposed to UVA and UVB rays, it produces a brown pigment called melanin (which appears as a tan). If the skin goes unprotected, sunburns can happen. The Canadian Dermatology Association thinks that unprotected skin can become damaged after 30 minutes in the sun. Mild sunburns redden the skin; they appear up to 24 hours after sun exposure and fade within 3-5 days. Serious sunburns can result in a painful blistering and peeling of the skin. The damage from sunburns does not disappear, but rather builds up through the years.

Sun protection factor (SPF) refers to the ability of the sunscreen or sunblock product to protect the skin from ultraviolet rays for a certain length of time. SPF gives people an idea of how much protection they're actually getting by comparison with the amount of time it takes for unprotected skin to burn.

In the best-case scenario, if it normally takes 10 minutes for skin to burn, an SPF of 15 would protect the person for fifteen times longer (two and a half hours), assuming that the sunscreen is reapplied frequently (which is not usually the case). For best results, sunscreen should be reapplied every two hours or after swimming or sweating. Most people do not reapply sunscreen regularly, which means most people are not getting the maximal protection from their sunscreen!

A higher SPF number means that the sunscreen protects the skin for a longer period of time. For example, SPF 60 sunscreen will protect the skin four times as long as SPF 15 sunscreen, or 60 times as long as no sunscreen at all.

The Canadian Dermatology Association recommends using a sunscreen with a minimum SPF of 30. People who have different needs may require a higher SPF. The sunscreen should also be broad-spectrum (meaning it blocks both UVA and UVB). Many sunscreens are endorsed by the Canadian Dermatology Association; look for their logo on the packaging. Ask your pharmacist to help you choose a good sunscreen for you.

Sunscreen should be applied liberally on dry skin, about 15-30 minutes before going out into the sun. Most people do not apply enough sunscreen, which again means that they are not getting maximal protection! Here are some general guidelines on how much to use:

  • The entire body can be covered with about 30 mL (a full shot glass) of sunscreen. A bottle containing 120 mL (4 ounces) should last four complete applications.
  • The head and neck can be covered with just over a half teaspoon of sunscreen.
  • The arms and legs can be covered with one teaspoon each of sunscreen.
  • The chest, stomach area and back can be covered with 3 teaspoons of sunscreen.

Don't forget the upper back, lips, tips of the ears, nose, and neck. These are commonly-missed areas where most cancers occur. Another thing to keep in mind is that avoiding direct sunlight, wearing clothing and hats to cover up, and putting on sunglasses will all protect you from the sun. Sunscreen should be used in addition to, and not instead of, these basics.

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