The link between skin cancer and accelerated aging with sun exposure is indisputable and much well designed research and observations have proved this. Taking out the aging aspects, UV exposure is the single most important causing factor for the majority of skin cancer. UV rays can be separated into UVA, UVB and UVC, depending on the wavelength. The relevant ones to skin are UVA and UVB as these are the two that reach the earth’s surface.

Effects of UV

The effects of UV radiation on the skin include short-term redness, inflammation, burn and tanning. The chronic, long-term effect that we see years later include the altering of skin immunity, aging and cancer. You may be able to see these differences when comparing heavily sun exposed sites (face, neck, arms) with skin that get little light (inner thighs, inner arms, abdomen). The visible changes in the skin include roughness, wrinkles, uneven tone and pigmentation, tiny blood vessels (telangiectasia), rough and pink patches (that may represent a pre-cancerous lesion). Protection from the sun will reduce the development of such signs. Sun protection goes beyond sunscreen lotion. It includes sun avoiding behaviour and protective clothing.

What Does SPF Mean?

Sunscreens use the SPF rating, which is defined as the UV dose required to develop a minimum erythema dose (MED) after an application of 2mg/cm2 of sunscreen. SPF 10 means that it can absorb 10x the dose of UV radiation before developing redness (erythema) compared to if you did not use the sunscreen. So if the intensity of UV generated at mid-day causes you to go red in 10 minutes, then the SPF 10 means that under the same conditions, you will get to the same redness in 100 minutes. SPF indicates protection from UVB rays with UVA effect more unpredictable. Your sunscreen will protect from UVB as standard, but not all will protect from UVA.

Types of Sunscreens

There are 2 main types of sunscreens – organic and inorganic. Organic ones, sometimes called chemical filters, absorb the UV radiation and re-emit it as heat. Inorganic ones, also called physical blockers, are made of particles that scatter and reflect the rays. Most commonly, these will be zinc oxide and titanium dioxide. The main problem with this type is that they have the telltale whiteish powder residue, but newer formulations can get around this problem to some extent. They also impart fewer irritant issues for those with sensitive skin. The latest sunscreens also contain anti-oxidants to reduce free radical damage (see other article on the causes of skin aging). They may contain plant derivatives or anti-oxidant vitamins.

How to Use Sunscreens

The recommendation is to wear a sunscreen every single day, regardless of whether the sun seems to be out or not. They should be applied half an hour before leaving the house and all sun-exposed areas covered. Ideally, it should be re-applied during the day, although understandably this may be impractical for some. The FDA recommends re-applying at least every 2 hours, more frequently if you have sweat a lot or have been in water.

Daily sunscreens should contain at least SPF 30 and be broad spectrum (meaning it covers UVA as well as UVB). At high level exposures (during beach holidays), then SPF 50+ should be applied and stricter re-application routine should be followed. Those with pigmentation issues (such as sun-spots, melasma or scar pigmentation), should also wear SPF 50 daily.