Sunlight is made up of many different waves or rays. One group of sunlight rays is visible light. Visible light is safe and necessary for life. Most of the other sunlight rays are dangerous. The majority of these are blocked by the earth\'s atmosphere. The part of the atmosphere that blocks many of these dangerous rays is the ozone layer. X-rays and gamma rays are examples of dangerous sunlight rays which are completely blocked by the ozone layer. Other dangerous rays such as ultraviolet light are only partially blocked by the ozone layer. Ultraviolet light is divided into three types: UVA, UVB and UVC. UVA rays are only slightly blocked by the ozone layer and can pass through window glass. The bulbs in tanning booths produce UVA type rays. UVA rays cause skin tanning, age spots and wrinkling of the skin, and contribute to the development of skin cancer. UVB rays are partially blocked by the ozone. UVB rays cause sunburn, basal cell skin cancer, squamous cell cancer and malignant melanoma, a deadly form of skin cancer. The third type of ultraviolet light, UVC, does not reach the earth\'s surface. It is blocked by the ozone layer. The sun is not the only source of ultraviolet rays. Many offices and factories use bulbs which emit low levels of UVA and UVB rays. Indoor fluorescent lighting can contribute up to 20% of one\'s ultraviolet dose in the northern United States. Ultraviolet rays have many harmful effects. Ultraviolet rays destroy plants, cause cataracts (a common form of blindness), lead to the development of skin cancer and cause premature aging of the skin. If you do not believe that ultraviolet light causes aging of the skin, then compare the skin on the back of your hands to the skin on your inner thigh or buttocks. As we grow older we develop brown marks, wrinkles and thinning of the skin on the areas of the skin which are exposed to sunlight. These changes can most readily be seen in people over fifty years of age. These same areas are also the sites of skin cancer. Most skin cancers occur on the face. Skin cancer almost never occurs on the buttocks, under the arms or on the inner thighs. The skin has several defense systems to help protect it from ultraviolet rays. The most important of these is the pigment or color of the skin. The skin is made of building blocks called cells. One type of skin cell, the melanocyte, produces a chemical called melanin. Melanin is a chemical or pigment which determines the color of the skin. Both blacks and whites have the same number of melanocytes, but in blacks, the melanocytes produce larger globules of pigment which causes their skin to be darker. The skin color or melanin protects the skin from the harmful effects of ultraviolet light. The extra melanin or color in an African-American\'s skin is equivalent to a white person wearing a sunscreen with an SPF of 45. Most black people look ten years younger than their white counterparts because of this increased protection. When the skin is exposed to ultraviolet light, it is injured and responds by making more color or melanin. This causes the skin to turn brown or tan. When the skin tans, this is evidence that the skin has been damaged by ultraviolet light. There is no such thing as a safe way to tan. Tanning is a process in which skin injury is occurring. There is no physical need or benefit for people to expose their skin to ultraviolet light (sunbathe). The only benefit from exposing the skin to sunlight is for vitamin D production. When sunlight hits the skin, it helps the body make vitamin D. Most people obtain plenty of vitamin D from fortified milk. If you take a multivitamin each day or eat a healthy diet, there is no reason to lie in the sun. One should never indulge in sunbathing. Sunbathing is a social disease like drinking alcohol or smoking cigarettes. Apply a sunscreen of SPF 15 or greater every day as a regular habit beginning at an early age. Each morning one should apply sunscreen to all skin that is exposed to sunlight. This will also help protect you from the ultraviolet light bulbs found in most work environments. Those who have light skin, red or blond hair, blue eyes and freckles have a poor tolerance to sunlight. If you fall into one of these groups, you need to be extra careful. When outside during the summer months, wear protective clothing. Protective clothing is dark and has a tight weave. Dark clothing blocks more sunlight from getting to the skin than light colored clothing. When outside, wear a wide brim hat or remain under an umbrella. A myth regarding sunlight exposure is that on a cloudy day you cannot get sunburned. This is incorrect, because ultraviolet light can penetrate clouds. Also most people believe that if the sun is not directly shining on you, you will not get burned. However, a person sitting under an umbrella on the sand can be burned by the sunlight\'s reflection from the sand. The majority of ultraviolet rays hit the earth during the middle of the day from 10 a.m. to 3 p.m. Avoiding sun exposure between these times will reduce the harmful effects of sun exposure. In summary, tanning is a very unhealthy and dangerous recreational activity that should be avoided. One\'s daily skin care regimen should consist of applying a sunscreen of SPF 15 or higher to all areas of exposed skin such as the face, neck, and back of the hands and avoiding unnecessary sun exposure. This regimen will help keep you looking younger and prevent skin cancer.