Description:Infection in a wound is usually due to bacteria. The most common are streptococcus ("strep") and staphylococcus ("staph"). Infection can be local ("cellulitis"), streaking ("lymphangitis" or "blood poisoning"), or pus-forming ("boil" or abscess). The most dangerous infections occur in wounds where there is dead tissue -- for example gas gangrene and tetanus.This boy stuck a needle into a burn blister on his palm yesterday. Note the redness and the streaking.

Lymphangitis is a streaking infection. Look for a red band going upstream the wound. This infection is usually caused by strep, often in combination with staph.This girl waded barefoot through a mountain stream, cutting the bottom of her foot on broken glass. The wound is now more painful. See the small red streaks heading around the foot. Lymphangitis always goes towards the heart.

This is a "pustule." This type of infection occurs when germs grow between the skin layers, raising up a "blister" of pus.This biker got a "puncture weed" in his shoe yesterday. Today there's a pustule on the bottom of his foot. And can you see the slight pink streak heading across the underside of the arch of the foot?

"Cellulitis" is local infection without streaking. It's painful, red, and swollen.This girl borrowed biking shoes that were too small. After wearing a hole in her toe, she did nothing to protect the wound. Today, the toe is swollen, tender, pink, and oozing.

Infection can result from a foreign body in a wound.This biker ran a puncture-weed thorn into his thumb tip during a fall over a week ago. It's still sore, and the puncture wound won't heal. Notice the whitish bulge between the thumbnail and the wound. This is a foreign body infection. A wound that refuses to heal is often contaminated or infected.

A "boil" is a small abscess or collection of pus just under the skin. When they occur without a wound, it's usually due to bacteria in a hair follicle breaking out into the fatty tissue. It often happens in an area of chafing.This biker has a boil at the belt line, caused by riding with pants that were stiff and rubbed the skin.

Not all infections are bacteria. Fungi and viruses can also infect wounds.This young woman had a tiny cut on her finger. Her boyfriend had a cold sore. When the cut seemed almost healed, it suddenly erupted with many painful pustules. This is a herpes simplex (cold sore virus) infection of the skin.