Ingrown hairs happen when a hair grows back into the skin instead of rising up and out of the follicle. This triggers an inflammatory reaction, producing those familiar red, tender bumps that can appear anywhere you shave, wax, or pluck. The underlying causes range from the shape of your hair follicle to how you remove hair and what you wear afterward.
How Hair Grows Back Into the Skin
There are two distinct ways a hair becomes ingrown, and both end with the hair piercing skin it shouldn’t.
The first is called extrafollicular penetration. After shaving, the freshly cut hair has a sharpened tip. If that hair is even slightly curly, it curls back toward the skin surface a short distance from the follicle opening and pierces the outer layer of skin. It then keeps growing downward, burrowing deeper.
The second is transfollicular penetration. Here, the hair never makes it out of the follicle at all. The growing tip curves downward inside the follicle and punctures the deeper layer of skin (the dermis) from within. Your body treats this buried hair like a foreign invader, launching an inflammatory response that causes redness, swelling, and sometimes pus.
Why Curly and Coarse Hair Is More Prone
Hair structure is the single biggest risk factor. A curved hair follicle produces tightly curled hair, and that curl encourages the hair to re-enter the skin once it’s been cut and starts growing back. Coarse hair compounds the problem because thicker strands have more rigidity, giving them the physical force to puncture skin. People with naturally curly or coarse hair are disproportionately affected, and chronic ingrown hairs in the beard area are common enough to have their own medical name: pseudofolliculitis barbae.
Straight, fine hair can still become ingrown, but it happens far less frequently because the hair shaft tends to grow away from the skin rather than curving back toward it.
How Hair Removal Creates the Problem
Shaving is the most common trigger. A razor blade creates a sharp, angled edge on the cut hair, making it easier for the tip to pierce skin. Single-blade razors cut hair at the skin’s surface, leaving a pointed shaft that can curl back in. Multi-blade razors introduce an additional issue: the first blade pulls the hair slightly outward so the second blade can cut it below the skin’s surface, producing a closer shave. When that hair retracts beneath the skin after cutting, it has no choice but to grow through tissue to reach the surface again.
Waxing and tweezing cause ingrowns through a different route. When hair is pulled from the root, the new hair growing in is finer and may lack the strength to push through the follicle opening, especially if dead skin cells have accumulated over it. The hair curls inside the follicle and grows sideways or downward.
Shaving against the direction of hair growth, stretching skin taut while shaving, and dry shaving all increase the odds. Each of these practices either cuts hair shorter than intended or creates a sharper edge on the remaining shaft.
Tight Clothing and Friction
What you wear after hair removal matters. Tight clothing rubs against skin, and that constant friction can push freshly cut hair tips back into follicles or irritate follicles that are already vulnerable. The problem gets worse in hot, humid conditions. When skin is damp and warm, hair follicles are easier to damage, and the combination of moisture, heat, and pressure from clothing creates ideal conditions for ingrown hairs. This is why ingrowns are so common in the bikini area, along the waistband, and on the inner thighs.
Hormones and Hair Growth Patterns
Androgens, particularly testosterone, stimulate hair growth, increase hair thickness, and darken hair color. When androgen levels are elevated, hair grows faster, denser, and coarser in areas that are frequently shaved or waxed. Conditions like polycystic ovary syndrome (PCOS) and congenital adrenal hyperplasia can drive androgen production higher than normal, causing coarse, dark hair to grow in areas where it previously didn’t. More coarse hair in more places means more opportunities for ingrowns, especially when those areas are subject to regular hair removal.
Dead Skin and Clogged Follicles
A buildup of dead skin cells over the follicle opening can trap hair beneath the surface. Without a clear path out, the growing hair diverts sideways or curls back on itself. This is why exfoliation plays such a central role in prevention. Chemical exfoliants that dissolve the bonds between dead skin cells, particularly salicylic acid at around 2% concentration, can keep follicle openings clear. Glycolic acid works similarly by dissolving the surface layer of dead skin, though concentrations above 10% can irritate sensitive areas.
People with naturally dry skin or those who don’t exfoliate regularly are more likely to develop the kind of surface buildup that blocks follicles. The same applies after waxing, when the follicle opening can seal over with new skin before the hair has a chance to emerge.
What Happens When Ingrowns Get Worse
Most ingrown hairs resolve on their own once the hair breaks through the skin or is gently freed. But when they don’t, the persistent inflammation can lead to real complications. The bump can become secondarily infected with bacteria, turning a simple ingrown into a painful, pus-filled abscess. Repeated ingrowns in the same area can cause post-inflammatory hyperpigmentation, leaving dark spots that last months after the bump itself is gone.
The most significant long-term risk is scarring. Chronic ingrown hairs produce a foreign body reaction, where the immune system continually attacks the trapped hair. Over time, this can result in permanent scarring, sometimes in grooved patterns across the skin. In some cases, the scarring becomes raised and firm, forming keloids that extend beyond the original site of inflammation. People prone to keloid formation are especially vulnerable to this outcome, and once keloid scarring develops, it’s difficult to treat.
Where Ingrown Hairs Are Most Common
Any area where hair is removed can develop ingrowns, but certain spots are far more susceptible. The beard and neck are the most frequent sites in men, where coarse, curly facial hair meets daily shaving. In women, the bikini line and groin area top the list, followed by the underarms and legs. These areas share common traits: the hair tends to be coarser, the skin folds or creases, and clothing creates friction over freshly shaved skin. The back of the neck, where barber clippers cut hair very short, is another frequent trouble spot.