Patchy hair loss is most commonly caused by alopecia areata, an autoimmune condition that affects roughly 2% of the global population. But several other conditions can create a similar pattern of distinct bald spots, including fungal infections, hair-pulling habits, tight hairstyles, and even sexually transmitted infections. Figuring out the cause matters because some forms are reversible and others, if left untreated, can become permanent.
Alopecia Areata: The Most Common Cause
Alopecia areata is an autoimmune condition where your immune system mistakes hair follicles for a threat. Normally, hair follicles have a kind of built-in shield that keeps immune cells from attacking them. When that shield breaks down, immune cells swarm the follicle and shut down hair production. Skin biopsies from people with alopecia areata show dense clusters of these immune cells packed around and inside hair follicles, along with elevated levels of inflammatory signals that amplify the attack.
The result is one or more smooth, round bald patches that appear suddenly, often on the scalp but sometimes in the beard, eyebrows, or elsewhere on the body. The patches tend to have well-defined borders and smooth skin with no redness or scaling. A hallmark clue is “exclamation point” hairs at the edges of the patch: short, broken-off strands that are narrower at the base, giving them a tapered look.
Peak onset falls between ages 20 and 34, though it can start at any age, and it’s slightly more common in women. Lifetime risk sits between 1.7% and 2.1%. Some people experience a single episode that regrows on its own within months. Others have recurring patches, and a smaller number progress to total scalp or body hair loss. Stress, other autoimmune conditions like thyroid disease, and family history all raise the likelihood.
Treatment has changed significantly in recent years. Three JAK inhibitor medications are now approved in the United States for severe cases. These drugs work by blocking the specific inflammatory signaling pathways that drive the immune attack on hair follicles. They represent the first targeted therapies for alopecia areata, and they’ve shown meaningful regrowth in clinical trials for people who’ve lost 50% or more of their scalp hair.
Fungal Scalp Infections
Tinea capitis, a fungal infection of the scalp, is the second major cause of patchy hair loss, particularly in children. Unlike alopecia areata, fungal patches are scaly, crusty, or inflamed. There are three recognized types: gray patch, black dot, and favus.
In the United States, the black dot type is most common and is caused by a fungus called Trichophyton tonsurans. It creates one or more scaly patches where hairs break off right at the skin surface, leaving tiny dark dots visible on the scalp. A less common type, caused by Microsporum canis, coats the outside of the hair shaft and glows green under a special ultraviolet light that dermatologists use in the office. Tinea capitis spreads through shared combs, hats, pillows, and direct contact, so it often affects multiple children in the same household or school.
The key difference from autoimmune hair loss is the presence of scaling, itching, or tenderness. If you see flaky, irritated skin within a bald patch, a fungal infection is a strong possibility. Oral antifungal treatment is required because topical creams can’t penetrate deeply enough to reach the fungus inside the hair shaft. With proper treatment, hair typically grows back fully.
Traction Alopecia From Tight Hairstyles
Chronic tension on hair follicles can create patchy thinning or bald spots, especially along the hairline, temples, and the area around the part. Styles that commonly cause this include tight cornrows, locs, braids, buns, ponytails, weaves, hair extensions, and rollers worn to bed regularly. The constant rubbing of hats or headscarves over tightly pulled hair adds to the damage.
People of African descent face higher risk because the natural shape of their hair follicles makes the strands more vulnerable to breakage from tension. Early on, you might notice soreness at the scalp, small bumps around the hairline, or baby hairs that stop growing back. At this stage, the damage is reversible if you switch to looser styles.
When pulling continues for months or years, the follicles scar over and the skin in those areas becomes smooth and shiny. Once traction alopecia reaches this stage, regrowth is no longer possible. That timeline makes early recognition critical.
Hair-Pulling Disorder
Trichotillomania is a behavioral condition where a person repeatedly pulls out their own hair. It creates patchy bald areas, but the pattern looks different from alopecia areata. Instead of smooth, well-defined circles, the patches tend to have irregular shapes with hairs of varying lengths, since newly growing strands get pulled out at different stages. There’s usually no scaling or redness unless the skin has been damaged by repeated pulling.
The pulling often targets the scalp but can also involve eyebrows, eyelashes, or body hair. Many people with trichotillomania aren’t fully aware of the behavior, especially when it happens during activities like reading, watching television, or lying in bed. Over time, chronic pulling can cause scarring, infections, and permanent follicle damage in the affected areas.
Secondary Syphilis
A less well-known cause of patchy hair loss is secondary syphilis, which can produce a distinctive “moth-eaten” pattern on the scalp. This looks like scattered, irregularly bordered patches of thinning rather than the clean circles of alopecia areata. The bald areas often cluster around the back and sides of the head.
Under magnification, the affected areas show empty follicles, short regrowing hairs, fewer hairs per follicular unit, and a reddish background. This pattern is considered a hallmark sign of the infection. Syphilitic hair loss usually appears alongside other symptoms of secondary syphilis, such as a body rash, mouth sores, or swollen lymph nodes. A blood test confirms the diagnosis, and antibiotic treatment resolves both the infection and the hair loss.
Scarring vs. Non-Scarring Hair Loss
One of the most important distinctions your doctor will make is whether the hair loss is scarring or non-scarring, because this determines whether regrowth is possible. In non-scarring types like alopecia areata, the follicle openings are still visible on the skin’s surface, even within the bald patch. The follicles are dormant but intact, which means they can potentially restart production.
In scarring types, the follicle openings disappear entirely as scar tissue replaces them. The skin may look smooth, pale, or slightly shiny. Clinical inflammation like redness, tenderness, or pustules is often present, though not always. Several inflammatory skin conditions can cause scarring hair loss, including lichen planopilaris and discoid lupus. These require different treatment approaches because the goal shifts from stimulating regrowth to stopping the scarring process before more follicles are lost.
Visual examination alone isn’t always reliable for telling these apart. The medical literature is full of examples where one type mimicked another, so a scalp biopsy is often the most definitive way to confirm what’s actually happening beneath the surface.
How to Tell the Causes Apart
A few visual clues can help narrow down what’s behind patchy hair loss before you see a doctor:
- Smooth, round patches with no scaling: most likely alopecia areata, especially if you notice tapered “exclamation point” hairs at the edges.
- Scaly, crusty, or itchy patches: suggests a fungal infection, particularly in children.
- Thinning along the hairline or temples: points toward traction alopecia if you regularly wear tight hairstyles.
- Irregular patches with hairs of different lengths: characteristic of trichotillomania.
- Scattered, moth-eaten thinning with a reddish background: raises concern for syphilis, especially with other systemic symptoms.
- Shiny, smooth skin with no visible follicle openings: indicates a scarring process that needs prompt evaluation.
A dermatologist can perform a gentle hair pull test, where a small group of hairs is tugged to see how easily they release, and may use a dermatoscope to examine the follicles at high magnification. These simple office tools, sometimes combined with a biopsy or blood work, usually pinpoint the cause and guide the right treatment.