Acne keloidalis nuchae (AKN) develops when hair follicles on the back of the neck become damaged, triggering chronic inflammation that eventually produces thick, scar-like bumps. The exact cause isn’t fully understood, but the condition results from a combination of mechanical irritation, hair texture, hormonal factors, and in some cases, certain medications. It is 20 times more prevalent in men than in women, and it primarily affects men of African descent with afro-textured hair.
How the Condition Develops
AKN starts with damage to hair follicles in the occipital region, the lower back of the scalp and nape of the neck. When a follicle is injured or a hair shaft curves back into the skin, the body mounts an immune response. White blood cells flood the area around the damaged follicle, creating small, firm, dome-shaped bumps that are typically 2 to 4 millimeters across.
If the irritation continues, hair shafts break free from their follicles entirely and become trapped in the surrounding skin. The body treats these loose hairs like foreign objects, intensifying inflammation and producing dense scar tissue. Over time, individual bumps can merge into thickened, band-like plaques along the hairline or, in severe cases, large tumor-like masses. Once this scarring takes hold, the affected follicles are permanently destroyed, and hair no longer grows from those sites.
Mechanical Irritation and Friction
Repeated physical trauma to the back of the neck is one of the most consistently identified triggers. Close-shaved haircuts are a major culprit: when hair is cut very short, the sharpened tip of a curly hair shaft can re-enter the skin as it grows, setting off the inflammatory cycle. Barber techniques that shave against the grain or use straight razors at the neckline are particularly problematic.
Friction from clothing and equipment also plays a significant role. Tight shirt collars, caps, and helmets have all been implicated as considerable risk factors. In military populations, AKN is common enough that severe cases can disqualify service members from meeting grooming and equipment standards, since the condition can interfere with properly wearing Kevlar helmets. Athletes who wear snug-fitting headgear face similar risks. Any object that rubs repeatedly against the nape of the neck can initiate or worsen the condition.
Hair Texture and Structure
The strong association between AKN and afro-textured hair points to follicle shape as a key contributing factor. Tightly coiled hair grows from curved follicles set at sharp angles in the skin. When this hair is cut short, the curling shaft is more likely to pierce back into the skin surface rather than growing outward. This creates the ingrown hairs that spark the initial inflammation.
This structural predisposition explains why AKN is estimated to account for between 0.45% and 13.6% of all skin conditions diagnosed in individuals of African descent, a remarkably wide range that reflects differences across geographic regions and study populations. The condition does occasionally appear in people of other backgrounds, but it is far less common.
Hormonal Factors
AKN overwhelmingly affects men, and it typically begins after puberty, both of which suggest that androgens (male sex hormones) play a role. The back of the neck is a hormone-sensitive area where androgens influence hair growth patterns, follicle size, and oil production. Higher androgen activity may make follicles in this region more prone to the type of inflammation that drives AKN. The condition is rare in women and in prepubescent boys, reinforcing the hormonal connection.
Medications That Can Trigger AKN
Certain drugs are documented triggers. Cyclosporine, an immunosuppressant used after organ transplants and for autoimmune conditions, has been linked to AKN development. Two anti-seizure medications, diphenylhydantoin and carbamazepine, are also associated with the condition. If you’re taking one of these medications and notice firm bumps forming on the back of your neck, it’s worth raising with your prescriber. Drug-related cases may improve when the medication is adjusted, though this isn’t always possible.
What AKN Looks and Feels Like
Early-stage AKN appears as small, firm bumps clustered at or just below the posterior hairline. They can be skin-colored, pink, or darker than the surrounding skin. Many people notice itching or tenderness before visible bumps appear. At this stage, the bumps are individual and spaced apart.
As the condition progresses, those discrete bumps begin to merge. The skin thickens into raised plaques with a rubbery or woody texture. Some bumps develop pustules on top, which can drain. In advanced cases, large masses form that can extend well beyond the nape of the neck. Hair loss in the affected area is permanent once scar tissue replaces the follicles. The progression from early bumps to significant scarring can take months or years, and it often depends on whether the mechanical triggers continue.
Reducing Your Risk
Because so many triggers are mechanical, practical changes can make a real difference, especially if you catch the condition early. Avoiding very close shaves on the back of the neck is one of the most effective steps. Using clippers with a guard rather than razors leaves hair long enough that it’s less likely to curve back into the skin. If you visit a barber regularly, ask them to leave the neckline slightly longer.
Minimizing friction matters too. Loosening shirt collars, avoiding tight-fitting hats, and limiting helmet use when possible all reduce irritation at the nape. For people whose jobs require helmets or high collars, keeping the skin clean, dry, and free of sweat buildup can help limit flare-ups. Letting your barber know you’re prone to AKN ensures they avoid aggressive techniques in the area, which is especially important since many people first notice symptoms shortly after a fresh haircut.