(See also Overview of Bacterial Skin Infections.)
Folliculitis is a type of small skin abscess that involves the hair follicle. Other types of abscesses may appear both on the skin surface and within the deeper structures of the skin without always involving a hair follicle. Most skin abscesses are caused by Staphylococcus aureus bacteria and appear to be pus-filled pockets on the skin surface. Recently, a strain of Staphylococcus that is resistant to previously effective antibiotics has become a more common cause. This strain is called methicillin-resistant Staphylococcus aureus (MRSA).
Sometimes the bacteria enter the skin through a hair follicle, small scrape, or puncture, although often there is no obvious point of entry. People who live in crowded conditions, have poor hygiene or chronic skin diseases, or whose nasal passages contain Staphylococcus are more likely to have episodes of folliculitis or skin abscesses. A weakened immune system, obesity, old age, and possibly diabetes are also common risk factors. Some people may have recurring episodes of infection for unknown reasons.
Doctors may try to eliminate Staphylococcus from people prone to recurring infections by instructing them to wash their entire body with antibacterial soap, apply antibiotic ointment inside the nose where the bacteria can hide, and take antibiotics by mouth.
Folliculitis is an infection of a hair follicle. It looks like a tiny red or white pimple at the base of a hair. There may be only one infected follicle or many. Each infected follicle is itchy or slightly painful, but the person otherwise does not feel sick.
Some people develop folliculitis after exposure to a poorly chlorinated hot tub or whirlpool. This condition, sometimes called “hot tub folliculitis” or “hot tub dermatitis,” is caused by the bacterium Pseudomonas aeruginosa. It begins anytime from 6 hours to 5 days after the exposure. Areas of skin covered by a bathing suit, such as the torso and buttocks, are the most common sites.
Some people develop mild folliculitis in areas subjected to moisture and friction, such as areas under sports equipment or on the buttocks.
Infected hairs easily fall out or may be plucked out, but new pimples tend to develop.
Sometimes stiff hairs in the beard area curl and reenter the skin (ingrown hair) after shaving, causing mild irritation and inflammation. However, there is no actual infection. This type of folliculitis is called pseudofolliculitis barbae.
Folliculitis is treated with antibacterial cleansers or antibiotics that are applied directly to the skin (topically). Large areas of folliculitis may require antibiotics taken by mouth. Hot tub folliculitis goes away in a week without any treatment. However, adequate chlorination of the hot tub or whirlpool is necessary to prevent recurrences and to protect others from infection. Folliculitis caused by ingrown hairs is treated by a number of methods with varying success. The person may need to temporarily stop shaving.
For severe, recurring folliculitis, doctors may take a bacterial culture (a sample of pus is sent to a laboratory and placed in a culture medium that allows microorganisms to grow). The results of the culture are used to guide the choice of antibiotic.
Skin abscesses are warm, painful, pus-filled pockets of infection below the skin surface that may occur on any body surface. Abscesses may be one to several inches in diameter.
Furuncles and carbuncles are types of skin abscesses.
Furuncles (boils) are tender, smaller, more superficial abscesses that by definition involve a hair follicle and the surrounding tissue. Furuncles are common on the neck, breasts, face, and buttocks. They are uncomfortable and may be painful when closely attached to underlying structures (for example, on the nose, ear, or fingers).
Carbuncles are clusters of furuncles that are connected to one another below the skin surface. If not treated, abscesses often come to a head and rupture, discharging a creamy white or pink fluid. Bacteria may spread from the abscess to infect the surrounding tissue and lymph nodes. The person may have a fever and feel generally sick.
Doctors diagnose skin abscesses based on their appearance. Sometimes, doctors send pus samples to a laboratory to identify the bacteria (called a culture).
A skin abscess may go away with application of warm compresses. Otherwise, a doctor treats an abscess by cutting it open and draining the pus. After draining the abscess, a doctor makes sure all of the pus has been removed by using an instrument to open any smaller pockets that have developed in the abscess cavity and washing out the pocket with a sterile saline solution. Sometimes the drained abscess is packed with gauze to prevent more pus from forming in the abscess cavity, which is removed 24 to 48 hours later. If the abscess is completely drained, antibiotics usually are not needed. However, if the person has a weakened immune system, the infection has spread into nearby skin (cellulitis), the person has many abscesses, or the abscess is on the middle or upper part of the face, antibiotics that kill staphylococci, such as dicloxacillin and cephalexin, are given. If doctors suspect MRSA is the cause, antibiotics that kill that organism, such as trimethoprim with sulfamethoxazole, clindamycin, or doxycycline, are given.
People who have recurring skin abscesses can wash their skin with liquid soap that contains special antiseptics and take antibiotics for 1 to 2 months.