The most common bacterial infections are caused by staphylococcus (staph) and streptococcus (strep). These bacteria normally live on the skin and cause no problems until an injury allows the bacteria into the skin.

Bacteria infect the skin through hair follicles and breaks in the skin caused by preexisting skin conditions, a puncture or scrape, a surgical wound, an insect or animal bite, a burn, or sunburn.

Skin infections can also develop from bacteria picked up from the soil, a contaminated pond, the ocean, or the hospital. Methicillin-resistant staphlococcus-aureas (MRSA) is a common staph bacterium that causes skin infections and is resistant to many commonly used antibiotics making MRSA difficult to treat.

Minor skin infections can cause a rash, a boil (a painful, pus-filled lump), or an abscess (a pocket of pus). Severe skin infections can destroy the infected tissues and cause a high fever and intense pain.

People with immune system problems are at particular risk of bacterial skin infections (1).

Minor to moderate bacterial skin infections are treated with oral and/or topical antibiotics. In some instances, severe bacterial skin infections are treated with intravenous antibiotics. Abscesses can be drained, and if need be, dead skin and tissues can be removed in a procedure called debridement.

Common bacterial skin infections consist of:

Impetigo

Impetigo is a common, contagious skin infection, caused by staph and strep bacterias that create honey-yellow, crusted sores and small fluid-filled blisters on the face, arms, and legs. The lesions are itchy and painful. Scratching can spread the infection. Impetigo is contagious.

Cellulitis

Cellulitis is a common infection of the deep layers of the skin. The infection spreads from the skin’s surface to the deeper layers, causing redness, pain, swelling, and heat, and can permanently damage the skin. It is often caused by strep or staph bacteria.

Folliculitis

Folliculitis is an infected and inflamed hair follicle. It can appear as tiny red or white pimples at the base of one or more hair follicles. It can itch and may be painful. The infected hair may fall out. In severe cases, skin abscesses can form below the skin. Folliculitis is common in people with acne, and shaving increases the risk of folliculitis. Often, it resolves without treatment, but severe infection can cause permanent hair loss.

Fungi live on the body where it is moist and warm, such as skin folds, between the toes, on the genitals, and under the breasts. The fungi live on the skin and rarely penetrate deeply.

Fungal infections can cause rashes in areas of infection and other body parts. Fungal infections are diagnosed by skin scrapings and cultures. They are treated with topical and oral antifungal medications.

Common fungal infections consist of: 

Ringworm

Ringworm is a fungal infection that spreads easily from skin-to-skin contact. It typically presents as a circular-shaped rash. It can affect the feet (athlete’s foot), groin (Jock itch), scalp, hands, toenails and fingernails.

Fungal nail infections

Fungal nail infections occur when the fungus attacks a fingernail, toenail, or nail bed. It is notoriously difficult to cure, and recurrence is common. Treatment courses with topical or oral medications are long, ranging from 3-12 months.

A virus is smaller than a fungus or bacterium. It can only infect the skin if it invades a living skin cell. Inside the cell, it replicates and takes control of the infected cells. Viral skin infections cause warts, shingles, herpes (cold sores), and other rashes. The integrity of the skin barrier can keep viruses out. If the virus gets into the cells, it triggers an immune system response. Additionally, many viruses can cause immune reactions that present as rashes, though they don’t directly infect the skin cells.

Common viral infections are:

Herpes simplex virus

The herpes simplex virus causes cold sores. Cold sores occur most commonly on the inside and outside of the mouth but can infect any body area.

Shingles

Shingles is a viral infection caused by the chickenpox virus also called the varicella virus. It can be extremely painful and debilitating. Shingles is a re-activation of the chickenpox virus that sits dormant in our nerves after a chickenpox infection but can reactivate for numerous reasons.

Parasites are tiny insects or worms that burrow into the skin to live or lay their eggs and live off the human host. Parasitic infections are usually confined to the outer layer of the skin. Bedbugs are parasites. Scabies are caused by a mite that burrows into the skin. Lice are insects that cling to hair follicles. They can infect the hair on the head, body, and pubic area. All parasitic infections are easily spread. They are treated with antiparasitic medications.

1. https://www.merckmanuals.com/home/skin-disorders/bacterial-skin-infections/overview-of-bacterial-skin-infections