UVA, which is the longest of the wavelengths emitted by the sun, can penetrate the skin more deeply than UVB. It plays a major role in skin aging and wrinkling (photoaging). In the past, we used to think that UVA does not cause significant damage in areas of the outermost skin layer (the epidermis) where most skin cancers occur. However, more recent students have demonstrated that UVA damages skin cells called keratinocytes in the basal layer of the epidermis, where most skin cancers occur. So UVA contributes to and may even initiate the development of skin cancers.

UVA is the dominant tanning ray. The process of tanning results from injury to the skin's DNA; the skin turns darker because it would be trying to lessen the extent of damage to its DNA. These mutations, in large enough numbers, can lead to skin cancer.

UVB is known to be the main wavelength that causes skin reddening and sunburn. It produces damage to the more superficial layers of the skin. It plays a key role in the development of skin cancer and a contributory role in tanning and photoaging. UVB rays do not significantly penetrate glass.

Here are a few practical preventive tips tp protect your skin against damage from the sun UV rays:

• Stay in the shade, especially between 10 AM and 4 PM.
• Avoid getting burns.
• Avoid tanning and UV tanning booths.
• Cover up with clothing, including a broad-brimmed hat and UV-blocking sunglasses.
• Apply broad spectrum (UVA/UVB) sunscreen, with an SPF of 15 or higher as part of your daily routine. If you expect to stay outdoor for a long time, then you should use a water-resistant, broad spectrum (UVA/UVB) sunscreen with an SPF of 30 or higher.
• When you go to the beach, apply sunscreen to your entire body 30 minutes before going outside. Reapply every two hours, or immediately after swimming or excessive sweating.