While shade is a potentially valuable means of protection from the damaging effects of the sun’s ultraviolet (UV) rays, not all shade is equally protective.
People can spend long hours in the shade while still receiving quite a lot of sun exposure and risking skin damage. This is because UVB rays, often considered the most harmful part of sunlight, can reach the skin indirectly. Indirect or diffuse UV light is radiation that has been scattered by the clouds and other elements in the atmosphere, and/or bounced back from UV-reflective surfaces like dry sand or concrete. We can rely only on deep shade (where we cannot see the sky and no UV penetrates) to offer truly complete protection.
Skin cancers are disproportionately concentrated on the head compared with other parts of the body. Faces, the nose in particular, are especially at risk. For men, the ears are a focal point for melanoma, the deadliest form of skin cancer. Although the head is easy to protect, too often it is left bare. Even when hats are worn, many provide only minimal shade – especially for the nose, ears, and neck.
Hats with broad brims all around and those with brims angled downwards provide the greatest UV protection. Unless they are very large, umbrellas provide relatively little UV protection. A single umbrella on a sandy beach by the sea provides limited sun protection because so much UV is reflected under the umbrella from the surfaces of the sand, water and sky.
Shady trees are always inviting on a hot, sunny day, and those with large spreads of dense foliage best protect us from the sun. If you can, choose a tree near other trees or buildings to further block out the sky.
Factors that increase the amount of scattered or indirect UVB, such as reflective surfaces, will decrease the protection trees can provide. The same tree actually gives less protection earlier and later in the day, when the proportion of diffuse UV is high, than it does in the middle of the day when the sun is more directly overhead.
Shade structures such as roofed areas, shade-sails, and pergolas vary widely in the amount of protection provided. Factors that determine how well a structure provides shade include the size of the structure, its orientation, and where it is in relation to other structures, such as buildings, trees and other vegetation.
Shade alone can rarely provide full UV protection, especially for prolonged periods. However, it is one important element in a comprehensive sun protection program that includes covering exposed skin with clothing (particularly clothes made of bright- or dark-colored, tightly woven fabrics), wearing hats and sunglasses, and regularly using sunscreen containing zinc oxide and/or titanium dioxide with an SPF of 30 or higher.
All these steps taken together will help ensure that we are adequately protected from the sun’s rays when we are outdoors