Infected hair follicles, known medically as folliculitis, are most often caused by Staphylococcus aureus bacteria entering a damaged or blocked follicle. But bacteria aren’t the only culprit. Fungi, viruses, parasites, and even physical friction can all trigger follicle infections, and certain health conditions make them far more likely to recur.
Bacteria Are the Most Common Cause
The overwhelming majority of hair follicle infections are bacterial, and Staphylococcus aureus is the primary offender. This bacterium already lives on your skin. It becomes a problem when it gets past the follicle’s natural defenses, usually through a small break or irritation in the skin. Shaving, waxing, and tight clothing all create micro-damage that gives bacteria an entry point.
People who carry staph bacteria in their nasal passages are at higher risk for recurring infections, particularly around the beard area. Applying an antibiotic ointment inside the nostrils for five days can help eliminate this carrier state and break the cycle of reinfection.
A different bacterium, Pseudomonas aeruginosa, causes what’s commonly called “hot tub folliculitis.” This happens when you soak in water where chlorine or bromine levels have dropped too low to kill bacteria. Symptoms typically appear between 8 hours and 5 days after exposure as a sudden eruption of red bumps and pus-filled spots centered on hair follicles. The CDC recommends hot tubs maintain chlorine levels of at least 3 parts per million and bromine levels between 4 and 8 ppm. If you’re using a public hot tub, test strips are cheap and worth keeping on hand.
Fungal and Parasitic Infections
Not all follicle infections are bacterial. A yeast called Malassezia (the same organism behind dandruff) can overgrow inside hair follicles, especially in hot, humid conditions. This type of folliculitis looks a lot like bacterial folliculitis but won’t respond to antibiotics, which is one reason recurring bumps that don’t improve with standard treatment should prompt a closer look. Fungal folliculitis caused by Candida species also occurs, particularly in people taking broad-spectrum antibiotics that disrupt the skin’s normal microbial balance.
Tiny mites called Demodex live in nearly everyone’s hair follicles, particularly on the face and eyelashes. Two species matter here: one feeds on skin cells in smaller follicles, the other feeds on the oily sebum produced by glands near follicles. Normally these mites coexist with you without causing problems. They become an issue when your immune system can’t keep their population in check, allowing them to multiply and trigger inflammation. This is more common in people taking immunosuppressive medications, undergoing chemotherapy, or living with HIV.
Viruses Can Infect Follicles Too
Viral folliculitis is less common but worth knowing about because it looks different from the bacterial version and requires different treatment. The varicella-zoster virus (the same one behind chickenpox and shingles) is a more frequent cause of viral folliculitis than herpes simplex. In a study of 21 cases of herpes folliculitis, 17 were caused by varicella-zoster and only 4 by herpes simplex type 1.
What makes viral folliculitis tricky is that it often doesn’t look like a typical herpes outbreak. Two-thirds of cases in that study lacked the characteristic blisters or pustules you’d expect. Instead, the infection presents as inflamed follicles with surrounding redness, making it easy to mistake for a bacterial infection. In shingles-related cases, the follicles may be the only thing affected, with the surrounding skin surface looking relatively normal.
Physical Damage and Friction
You don’t always need an infectious organism to end up with inflamed, infected follicles. Physical damage to the follicle is one of the most common starting points. Shaving tops the list because it creates tiny cuts at the follicle opening while also pulling hairs to angles that encourage them to grow back into the skin. Waxing, tight braids, wigs, and heavy hair oils all stress follicles in different ways.
Friction from backpacks, helmets, and tight clothing (especially synthetic fabrics that trap moisture) occludes follicles and creates a warm, damp environment where bacteria thrive. Prolonged sitting can cause the same problem on the buttocks and thighs. Greasy sunscreens and heavy moisturizers can physically block follicle openings, trapping bacteria underneath.
There’s also a related condition called pseudofolliculitis barbae, commonly known as razor bumps, that’s worth distinguishing. This isn’t technically an infection. It happens when a curly hair either never exits the follicle or curves back into the skin after being cut, triggering a foreign-body reaction. It’s most common in people with tightly coiled hair and primarily affects the face and neck. It looks very similar to folliculitis but has a different underlying mechanism and requires different management.
Risk Factors That Make Infections More Likely
Some people get folliculitis once and never deal with it again. Others face repeated episodes. The difference often comes down to underlying risk factors.
- Weakened immune function: Diabetes, HIV, and immunosuppressive medications all reduce your body’s ability to fight off the bacteria and fungi that are always present on skin.
- Medications: Corticosteroids (including topical creams like hydrocortisone), broad-spectrum oral antibiotics, lithium, and androgen-based hormones all increase susceptibility. Antibiotics are a particular double-edged sword because they kill protective bacteria on the skin while leaving resistant organisms and fungi to fill the gap.
- Obesity and pregnancy: Both increase skin-on-skin friction, sweating, and moisture retention in skin folds.
- Occupational exposure: Working in hot, humid environments while wearing protective clothing creates ideal conditions for follicle occlusion. Contact with contaminated water, whether in pools, water slides, or through diving suits, raises the risk of Pseudomonas infections specifically.
How a Simple Infection Can Get Worse
Most superficial folliculitis shows up as a small tender or painless pustule around a hair and heals on its own without scarring. For mild cases, washing with an antimicrobial cleanser containing benzoyl peroxide and applying warm compresses is often enough.
The concern is when infection moves deeper. If bacteria invade the lower portion of the follicle, the bump becomes more swollen, painful, and red. These deeper infections can scar. When the infection extends beyond the follicle entirely, it becomes a furuncle (a boil), which is a painful, firm abscess originating from the follicle. Multiple connected furuncles form a carbuncle, a broad, deep, painful mass that drains through several openings. Carbuncles often come with fever and general malaise, which simple folliculitis almost never causes.
This progression from surface irritation to deep abscess is a continuum. The further it advances, the more likely you’ll need the infection drained rather than just treated with topical products. Recognizing early folliculitis and addressing it promptly, especially by keeping the area clean and avoiding further irritation, is the most effective way to prevent it from becoming something more serious.