There are many types of bacteria, both good and bad. In fact, most bacterial species cannot cause disease. Many species even play beneficial roles producing antibiotics and foodstuffs. The soil teems with free-living bacteria that perform many essential functions in the biosphere, like nitrogen fixation. As well, our bodies are covered with commensal bacteria that make up the normal flora. The skin is the body’s first barrier against bacteria that cause infections. Even though many bacteria live on the surface of our skin, healthy skin can usually protect us from infection. Bacterial skin infections can affect a small spot or may spread, affecting a large area. They can range from a treatable infection to a life-threatening skin condition. Many types of bacteria can infect the skin. The most common are Staphylococcus and Streptococcus. Skin infections caused by less common bacteria may develop in people while hospital sunless tan ized or living in a nursing home, while gardening, or while swimming in a pond, lake, or ocean. Bacteria usually enter through small breaks in the epidermis that result from scrapes, punctures, burns, and skin disorders. Areas of the skin that become swollen with fluid (edema) are especially vulnerable. Cellulitis is more common in people with poor blood circulation (chronic venous insufficiency). However, cellulitis can also occur in skin that is not obviously injured. Folliculitis is the inflammation of hair follicles due to an infection, injury, or irritation. It is characterized by tender, swollen areas that form around hair follicles, often on the neck, breasts, buttocks, and face. Boils are pus-filled lesions that are painful and usually firm. Boils are usually located in the waist area, groin, buttocks, and under the arm. Carbuncles are clusters of boils. These are usually found in the back of the neck or thigh.