Skin infections are caused by four types of organisms: bacteria, fungi, viruses, and parasites. Which one takes hold depends largely on whether your skin’s protective barrier has been compromised and how well your immune system can fight off invaders. In the United States alone, skin and soft tissue infections occur at a rate of roughly 78 per 1,000 people each year, making them one of the most common reasons for medical visits. Abscesses and cellulitis account for the majority of cases.
Your Skin Barrier Is the First Line of Defense
Healthy skin is remarkably good at keeping pathogens out. The outermost layer, a thin shield of tightly packed dead cells and natural oils, maintains a slightly acidic environment that discourages bacterial and fungal growth. When that barrier breaks, infections get their opening.
Disruption can be obvious, like a cut, scrape, surgical wound, or insect bite. But it can also be subtle. Harsh soaps strip away protective oils. Conditions like eczema raise the skin’s pH, which inactivates the enzymes that maintain the barrier and actually promotes the growth of harmful microorganisms. People with eczema often carry genetic changes that weaken this protective layer from the inside, creating a cycle of inflammation, dryness, and vulnerability to infection that feeds on itself.
Even something as simple as prolonged moisture, like sweat trapped in skin folds or a wet diaper, softens the barrier enough to let organisms in.
Bacterial Causes
Bacteria are the most common cause of skin infections. Two species do the bulk of the damage. Staphylococcus aureus is the usual culprit behind pus-forming infections like boils and abscesses. Streptococcus pyogenes typically causes spreading, red, non-pus infections like cellulitis and a deeper skin infection called erysipelas.
Both bacteria live harmlessly on many people’s skin or in their noses. They become a problem when they enter through a break in the barrier. A small nick from shaving, a hangnail, cracked skin between toes, or even microscopic damage from scratching can be enough. Community-acquired MRSA, a drug-resistant form of staph, has significantly increased the number of skin abscesses over the past two decades, particularly in children.
Bacterial skin infections range from minor (impetigo, a crusty rash common in kids) to serious (cellulitis spreading into deeper tissue). The type of infection often depends on how deep the bacteria penetrate and how your immune system responds.
Fungal and Yeast Causes
Fungal skin infections fall into two main categories. Dermatophytes, the fungi behind athlete’s foot, ringworm, and jock itch, feed on keratin, the protein in your skin, hair, and nails. They thrive in warm, moist environments, which is why these infections cluster in areas like the feet, groin, and scalp.
Yeast infections on the skin are most often caused by Candida, a type of yeast that naturally lives on your body in small amounts. It tends to overgrow in warm, moist, creased areas like the armpits, groin, and beneath the breasts. Diaper rash in infants is frequently a Candida infection, with the warm, damp environment inside the diaper creating ideal conditions.
Several factors tip the balance in favor of fungal overgrowth. Antibiotics kill off competing bacteria, giving yeast room to multiply. High blood sugar acts as fuel for yeast, which is why Candida infections are particularly common in people with diabetes. Steroid medications and chemotherapy also raise the risk by suppressing immune defenses. In adults, recurring or widespread Candida infections on the skin can sometimes signal an underlying immune problem.
Viral Causes
Viruses generally cannot infect intact skin. They need some form of barrier disruption to get in, whether that’s a tiny abrasion, a crack, or contact with a mucous membrane. Once they enter, different viruses behave in distinct ways that explain the types of lesions they produce.
Human papillomavirus (HPV) causes warts by infecting the deepest cells of the outer skin layer, requiring local trauma to expose those cells. It triggers excessive cell growth at the site, producing the raised, rough bumps most people recognize. Herpes simplex virus (HSV) takes a different approach, using specific receptor proteins on skin cells to enter even through minimal damage. After the initial infection, it retreats into nerve cells and goes dormant, periodically reactivating to cause recurring blisters, often in the same location.
Molluscum contagiosum, common in children, produces small, dome-shaped bumps and spreads through direct skin contact or shared surfaces like towels. Varicella-zoster virus causes chickenpox on first exposure and can reactivate decades later as shingles, producing painful blisters along a strip of skin that follows a single nerve path. Existing skin conditions like eczema or any form of inflammation make viral entry significantly easier.
Parasitic Causes
Parasites that affect the skin include mites and lice. Scabies is caused by a microscopic mite that burrows into the upper layer of skin, where the female tunnels just beneath the surface to lay eggs. The intense itching that follows, especially at night, is actually an allergic reaction to the mites and their waste, not the burrowing itself. This itching can persist for weeks after treatment, even after all mites are dead.
The scratching that scabies provokes frequently breaks the skin enough to allow bacteria in, leading to secondary bacterial infections. This is one of the most common complications of parasitic skin infestations and a good example of how one type of skin problem can open the door to another.
Conditions That Raise Your Risk
Some people get skin infections far more often than others, and underlying health conditions are a major reason why. The data is striking: people with no recorded health conditions develop skin infections at a rate of about 32 per 1,000 per year. For people with diabetes, that rate jumps to 165 per 1,000. Those with peripheral artery disease face a rate of 222 per 1,000, and people with a prior skin infection history are at the highest risk of all, at 281 per 1,000.
Diabetes creates a perfect storm for skin infections. High blood sugar feeds pathogens directly, nerve damage reduces sensation so injuries go unnoticed, poor circulation slows healing and limits immune cell delivery to the skin, and the immune cells themselves function less effectively. The elevated skin pH in people with diabetes further encourages yeast growth in skin folds. Chronic kidney disease, liver disease, and cancer also substantially increase risk, largely through immune suppression or poor circulation.
Age matters too. Adults 65 and older develop skin infections at roughly 125 per 1,000 per year, more than double the rate in younger adults. Aging skin is thinner, drier, heals more slowly, and produces fewer of the antimicrobial compounds that keep pathogens in check.
Signs an Infection Is Spreading
Most skin infections stay localized and resolve with appropriate care. But certain signs suggest an infection is moving beyond the skin into deeper tissue or the bloodstream. Fever developing alongside a skin wound or rash is one of the clearest signals. Expanding redness that moves outward from the original site, red streaks traveling away from a wound (following lymph channels toward the nearest lymph nodes), and swollen, tender lymph nodes near the infection all indicate the body is fighting a spreading process.
Rapidly worsening pain that seems out of proportion to what you see on the surface, skin that turns dusky or purple, or blisters forming around a wound can signal a deeper, more aggressive infection that needs urgent attention.
Prevention Starts With the Barrier
Protecting and repairing your skin barrier is the single most effective way to prevent skin infections. For minor wounds, cleaning with plain saline or clean water is the standard recommendation. Topical antibiotics and antiseptic agents are not recommended for routine wound prevention, as they can irritate tissue without meaningfully reducing infection rates.
Keeping skin moisturized prevents the microscopic cracks that let organisms in, particularly if you have eczema or naturally dry skin. Changing out of wet or sweaty clothing promptly, drying thoroughly between toes and in skin folds, and wearing breathable fabrics all reduce the warm, moist conditions that fungi and yeast need. For people with diabetes, daily skin checks, especially of the feet, catch small injuries before they become infected. Managing blood sugar directly reduces infection risk by removing the fuel that pathogens depend on and restoring some of the immune function that high glucose impairs.