Skin infections happen when bacteria, fungi, viruses, or parasites breach your skin’s outer barrier and multiply in the tissue underneath. That barrier can be broken by something as obvious as a cut or as subtle as the microscopic cracks that form between sweaty toes. Globally, bacterial skin infections alone account for roughly 170 million cases per year, making them one of the most common reasons people seek medical care.
How Bacteria Get In
The two bacteria responsible for most skin infections are Staphylococcus aureus (staph) and group A Streptococcus (strep). Staph lives harmlessly on the skin of about one in three people, waiting for an opening. Strep spreads through direct person-to-person contact, respiratory droplets, and wound discharge. Both can enter through cuts, scrapes, insect bites, surgical wounds, or even tiny breaks in dry or cracked skin that you can’t see with the naked eye.
Once inside, these bacteria cause infections ranging from minor (a small boil or impetigo patch) to serious (cellulitis, a spreading infection of the deeper skin layers that sends an estimated 14.5 million Americans to the doctor each year and costs $3.7 billion in outpatient care alone). The difference between a minor and serious infection often comes down to how deep the bacteria penetrate and how quickly your immune system responds.
A particularly stubborn form of staph, MRSA, spreads fast in athletic facilities, locker rooms, gyms, and health clubs because of shared equipment and direct skin-to-skin contact. You can pick it up by touching a contaminated surface and then touching a break in your skin. MRSA infections look like ordinary boils or pimples at first but can worsen quickly and resist common treatments.
Fungal Infections and Moisture
Fungi that cause skin infections feed on keratin, the protein that makes up your skin’s outer layer, your hair, and your nails. These organisms can live on your body permanently without causing problems. They cross the line into infection when conditions favor their growth: warmth, moisture, poor blood flow to the area, or a weakened immune system from conditions like diabetes, cancer, or HIV.
Athlete’s foot is the most common example. Sweat accumulates between your toes, creating the warm, damp environment fungi thrive in. You pick up the fungus by walking barefoot in communal showers, pool decks, or locker rooms where an infected person has been. Tight, poorly ventilated shoes make it worse by trapping moisture against the skin. The same family of fungi causes jock itch (in the groin) and ringworm (on the body or scalp), all spreading through the same combination of skin contact and favorable conditions.
Yeast infections of the skin work similarly. Candida, a yeast that naturally lives on your body, overgrows in skin folds where moisture gets trapped: under the breasts, in the armpits, or in the diaper area of infants. Anything that keeps skin consistently damp, from workout clothes left on too long to occlusive bandages, raises your risk.
Viral Skin Infections
Viruses cause a different category of skin infections, including warts, cold sores, and shingles. HPV, the virus behind common warts and genital warts, spreads through intimate skin-to-skin contact. A person can transmit it even without visible signs or symptoms, which is why warts seem to appear out of nowhere. You can also pick up the strains that cause common hand and foot warts by touching contaminated surfaces, especially in wet environments where the virus persists.
Herpes simplex, the virus that causes cold sores and genital herpes, also spreads through direct skin contact. It then hides in nerve cells and reactivates periodically, producing new sores on the same area of skin. Molluscum contagiosum, common in children, spreads the same way: skin touching skin, or skin touching a contaminated towel or toy.
Parasites That Burrow Into Skin
Scabies mites are microscopic parasites that burrow into the upper layer of your skin, where the female tunnels just beneath the surface to lay eggs. You can sometimes see these tiny burrow tracks as thin, irregular lines on the skin. Scabies spreads through prolonged skin-to-skin contact, which is why it moves quickly through households, nursing homes, and childcare centers. Sharing bedding or clothing with an infected person can also transmit it, though brief casual contact like a handshake is usually not enough.
Head lice and body lice work differently. They live on the surface of the skin or in clothing and feed on blood. Head lice spread almost exclusively through head-to-head contact, while body lice spread through shared clothing and bedding, particularly in crowded living conditions.
Common Entry Points
Your skin is remarkably good at keeping pathogens out when it’s intact. Infections happen when that barrier is compromised. The most common entry points include:
- Cuts, scrapes, and puncture wounds, even very small ones you might not notice
- Cracked, dry skin, especially on the hands and feet during cold weather
- Skin conditions like eczema or psoriasis, which create chronic breaks in the skin barrier
- Surgical sites and IV lines, which provide a direct path past the skin
- Insect bites, particularly when scratched open
- Spaces between toes, where moisture softens and breaks down the skin
Shaving also creates tiny nicks that bacteria can exploit, which is why razor bumps sometimes progress into folliculitis, an infection of the hair follicles.
Who Is Most at Risk
Anyone can get a skin infection, but certain factors make them significantly more likely. Diabetes is one of the biggest risk multipliers. Bacteria thrive when there’s too much glucose in the body, and fungal infections become more likely when blood sugar runs high. Diabetes also impairs circulation, which means less blood flow to the skin, slower healing, and drier skin that cracks more easily. The body even pulls fluid from its cells to produce enough urine to flush excess sugar, leaving the skin dehydrated and more vulnerable.
Other conditions that suppress the immune system, including HIV, cancer treatment, and long-term steroid use, reduce your body’s ability to fight off organisms that would normally be harmless. Obesity increases risk because skin folds trap heat and moisture. Poor hygiene, prolonged contact with contaminated water, and living in crowded conditions all raise exposure.
Environments Where Infections Spread
Certain places concentrate the conditions that skin infections need. Gyms and athletic facilities are high-risk environments because they combine shared equipment, skin-to-skin contact during sports, and warm, moist locker rooms. The CDC specifically flags these settings for MRSA transmission. Wrestling, football, and rugby carry elevated risk because of the amount of direct body contact involved.
Communal showers and pool decks are prime spots for picking up fungal infections. The warm, wet floors harbor dermatophytes shed by other people’s feet. Daycare centers and schools spread impetigo and scabies efficiently because children are in close physical contact throughout the day. Hospitals and long-term care facilities see higher rates of serious bacterial infections because residents often have weakened immune systems and broken skin from medical devices.
Practical Ways to Reduce Your Risk
Keeping your skin intact and dry handles most of the risk. Clean cuts and scrapes promptly and cover them until they heal. Dry thoroughly between your toes after bathing. Wear open-toed shoes or breathable footwear when possible, and change socks frequently in warm weather. Wear sandals in communal showers rather than going barefoot.
Avoid sharing towels, razors, or clothing with others, especially in athletic or communal living settings. If you use gym equipment, wipe it down before and after. Wash workout clothes after every use rather than letting them sit damp in a gym bag. For people with diabetes, keeping blood sugar well controlled is one of the most effective ways to prevent recurring skin infections. Moisturizing dry skin, particularly on the feet and hands, helps maintain the barrier that keeps pathogens out in the first place.