Skin. It is the largest organ of the body. Skin is the body’s【C1】______to infection. It keeps out many harmful【C2】______and othe

Skin. It is the largest organ of the body. Skin is the body’s first barrier to infection. It keeps out many harmful bacteria and other things. It also keeps all the things we need in our bodies. The skin helps control body temperature. Glands on the skin release fluid to cool the body when it gets too hot. When a person gets too cold, blood passages in the skin become narrow. This helps to trap heat inside the body.
   Like other organs of the body, the skin can have problems. Almost any teenager can tell you the most common disorder: acne. Acne is connected to hormones and how they affect the oil glands of the skin. The skin gets its oil, called sebum, from the sebaceous glands. Each gland connects to a passage of extremely small hairs. The sebum travels through these passages. The oil reaches the surface of the skin through little holes, called pores. Sometimes, the sebum, hair and cells of the pores block these openings. This is how acne starts.
   Bacteria can grow in a blocked pore. The bacteria produce chemicals and enzymes. White blood cells— infection fighters—travel to the area. All this leads to a growth on the skin, a pimple. This becomes red, hot and often painful. Some people think eating chocolate or oily foods causes acne. Others blame dirty skin or nervous tension. Yet researchers tell us none of these cause acne.
   So what does? Doctors are not sure. But they have some ideas. For one thing, they know that hormones called androgens are involved. Androgens cause the sebaceous glands to grow and make more oil.
   There are several treatments for acne. Mild cases are generally treated with medicines for use directly on the skin. These often contain salicylic acid or benzoyl peroxide. People with more serious acne may be given antibiotic drugs to take by mouth. Or they might use a combination of other treatments. Skin experts say there are simple ways to help prevent acne. One is to touch your face as little as possible, so as not to add oils or put pressure on the skin. Another good idea is to avoid the urge to burst pimples. This can leave permanent marks on the skin. Doctors also say to avoid strong cleaning products, and to be gentle as you wash and dry your skin.