Folliculitis develops when hair follicles become damaged or blocked, allowing bacteria, fungi, or other irritants to trigger inflammation. Almost any activity that creates friction, traps moisture, or breaks the skin around a hair follicle can set the stage. The specific cause determines where it shows up on your body, how long it lasts, and how to treat it.
How Bacteria Get Into Hair Follicles
The most common type of folliculitis is caused by Staphylococcus aureus, a bacterium that already lives on many people’s skin and inside their nasal passages. It enters through small scrapes, nicks from shaving, or tiny breaks in the skin you might not even notice. Sometimes there’s no obvious entry point at all.
Once the outer barrier of the follicle is compromised, bacteria settle into the opening and multiply. In superficial cases, inflammation stays near the surface of the follicle, producing small red bumps or whiteheads. In deeper infections, inflammation extends down the full length of the follicle and into the surrounding skin, which can lead to larger, more painful lumps. People who live in crowded conditions, have chronic skin problems, or carry Staph bacteria in their nose are more likely to deal with repeated episodes.
Hot Tubs and Contaminated Water
A different bacterium, Pseudomonas, thrives in warm water where chlorine or bromine levels have dropped too low. Soaking in a poorly maintained hot tub, heated pool, or whirlpool exposes your skin to this organism for a prolonged period, giving it time to colonize open follicles. The rash typically appears a few days after exposure and shows up in areas that were submerged, often the torso and buttocks.
Mild cases clear up on their own within a few days. To avoid it, the CDC recommends hot tub water maintain a chlorine level of at least 3 parts per million and a pH between 7.0 and 7.8. If you can’t verify the water quality, shorter soaks and a thorough shower afterward reduce your risk.
Shaving and Ingrown Hairs
Shaving is one of the most common everyday triggers. When a razor cuts hair at a sharp angle, the trimmed edge can curl back and pierce the surrounding skin as it regrows. This is especially common in people with curly or coarse hair, and it has a specific name: pseudofolliculitis barbae, commonly called razor bumps. It most often appears in the beard area but can develop anywhere you shave, including the legs, bikini line, and underarms.
The inflammation in this case isn’t caused by an infection. It’s a reaction to the hair itself acting as a foreign body inside the skin. Red, sometimes painful papules and pustules form around the ingrown hair. Shaving more frequently or against the grain makes it worse. The most effective prevention strategies include shaving in the direction of hair growth, using a clean and sharp razor, and applying shaving cream or gel to reduce friction. For people who get persistent razor bumps, switching to an electric trimmer that doesn’t cut below the skin surface, or stopping shaving entirely, often resolves the problem.
Fungal Overgrowth and Skin Mites
Not all folliculitis is bacterial. A yeast called Malassezia, which naturally lives on everyone’s skin, can overgrow inside hair follicles when conditions are right. Sweat, heat, and humidity fuel its growth. This type of folliculitis typically appears on the upper chest and back as clusters of small, itchy bumps that look a lot like acne but don’t respond to standard acne treatments. It’s often made worse by sweating during exercise or outdoor work.
Tiny mites called Demodex also live in hair follicles, and most people carry them without any symptoms. Problems arise when their population density gets unusually high. Research has found significantly elevated Demodex levels in people with rosacea, acne, and seborrheic dermatitis compared to people without these conditions. When mites overpopulate, they can trigger chronic low-grade follicular inflammation, particularly on the face.
Friction, Sweat, and Tight Clothing
Mechanical irritation is an underappreciated cause. Tight clothing, backpack straps, athletic gear, and anything that rubs repeatedly against skin can damage the outer layer of hair follicles, creating openings for bacteria or simply irritating the follicle enough to cause inflammation on its own. Combined with sweat and heat, the effect is amplified.
Folliculitis from friction and sweat tends to show up on the upper back, buttocks, and thighs. You’re more likely to develop it if you exercise heavily and don’t shower or change out of damp clothing soon afterward. Keeping skin clean and dry after sweating, and wearing breathable fabrics during physical activity, are the most practical defenses.
Medical Conditions That Raise Your Risk
Diabetes is one of the strongest medical risk factors for recurring folliculitis. Elevated blood sugar impairs blood flow to the skin and weakens the immune cells responsible for fighting off infections at the surface. Staph-related folliculitis and deeper infections called furuncles are among the most common skin problems in people with diabetes.
Any condition or treatment that suppresses the immune system increases vulnerability. This includes HIV, organ transplant medications, and long-term use of corticosteroids. A weakened immune response means the skin’s natural defenses are slower to contain bacteria or fungi that enter a damaged follicle, and infections tend to recur more frequently and take longer to resolve.
Medications That Cause Folliculitis
Certain drugs can trigger folliculitis as a side effect, accounting for roughly 1% of adverse skin reactions to medications. The most commonly implicated categories include systemic corticosteroids, some antibiotics (particularly those used for tuberculosis), lithium, immunosuppressants, oral contraceptives, anticonvulsants, and high-dose B vitamins (B1, B6, B12). A class of cancer drugs called EGFR inhibitors is also well known for causing widespread follicular eruptions, often on the face and upper body.
Drug-induced folliculitis looks similar to other forms but tends to appear in an unusual distribution or resist typical treatments. If you’ve started a new medication and notice a new crop of follicular bumps, that timing is worth noting for your provider.
Where It Tends to Show Up
Folliculitis can appear anywhere on the body that has hair, but certain types favor specific locations. The face, arms, upper back, and lower legs are the most common sites overall. Razor bumps concentrate in the beard area. Fungal folliculitis favors the chest and back. A less common type called eosinophilic folliculitis, which is linked to immune suppression, produces itchy pustules primarily on the shoulders, upper arms, neck, and forehead.
The pattern often hints at the cause. Bumps concentrated where clothing rubs suggest friction. A rash in areas covered by a swimsuit after a hot tub visit points to Pseudomonas. Persistent bumps on the chest and back that worsen in summer suggest yeast. Paying attention to location and timing is one of the most useful things you can do to identify your trigger and avoid it in the future.
Practical Steps to Prevent It
Most folliculitis prevention comes down to protecting hair follicles from damage and keeping skin clean. A few specific habits make a noticeable difference:
- Shave carefully. Use a sharp, clean razor and shave with the grain. Apply shaving cream or gel to minimize friction.
- Shower after sweating. Wash with a gentle soap after exercise or outdoor work. Don’t sit in damp workout clothes.
- Avoid sharing personal items. Towels, razors, and clothing can transfer bacteria between people.
- Check hot tub water quality. Ask about chlorine and pH levels before getting in, or use test strips if it’s your own.
- Wear breathable fabrics. Loose-fitting, moisture-wicking clothing reduces friction and trapped sweat, especially during physical activity.