Patches of hair loss are most commonly caused by alopecia areata, an autoimmune condition that affects roughly 1 in 50 people over their lifetime. But several other conditions can produce bald patches too, from fungal infections and tight hairstyles to stress-related hair pulling and scarring disorders. The pattern, location, and texture of the patches often point directly to the cause.
Alopecia Areata
Alopecia areata is the single most common reason people develop smooth, round bald patches on their scalp. It happens when the immune system mistakes hair follicles for a threat and attacks them during their active growth phase. Certain immune cells, primarily a type called CD8+ T cells, gather around the base of the hair follicle and release signaling molecules that disrupt the hair growth cycle. The follicle essentially gets forced into a resting state, causing the hair to fall out prematurely while also blocking new growth.
The patches typically appear suddenly. You might notice a coin-sized smooth spot on your scalp, or several at once. The skin in the patch looks normal, with no scarring, scaling, or redness. Some people experience a single episode that resolves on its own within months. Others develop recurring patches, and in a smaller percentage, the condition progresses to total scalp hair loss or even full body hair loss.
What triggers the immune system to turn on hair follicles isn’t fully understood, but genetics play a role, and episodes often follow periods of significant stress or illness. Alopecia areata is now treatable with a newer class of medications called JAK inhibitors, which work by blocking the immune signaling pathways that drive the attack on follicles. Two of these medications have been approved specifically for severe alopecia areata.
Fungal Scalp Infections
Tinea capitis, a fungal infection of the scalp, is one of the most common causes of patchy hair loss in children. The fungus invades hair shafts and weakens them until they snap off, leaving distinct patterns depending on the type of infection. In “black dot” tinea capitis, hairs break right at the scalp surface, leaving tiny dark dots where the stumps sit. In “gray patch” tinea capitis, short hair stubs remain visible above the surface.
Unlike alopecia areata, fungal patches are not smooth. You’ll typically see dry, scaly skin that resembles dandruff, along with redness and itching. In more inflammatory cases, painful swollen lumps called kerions can develop on the scalp. These may ooze pus and form crusts. Tinea capitis spreads through direct contact or shared items like combs and hats, which is why it runs through schools and households. It requires oral antifungal treatment because topical creams can’t penetrate the hair shaft deeply enough.
Traction Alopecia
Tight hairstyles are a surprisingly common cause of patchy hair loss. When hair is pulled in the same direction repeatedly, the constant tension damages follicles over time. The pattern of loss maps directly to where the force is greatest. Tight ponytails cause thinning at the front and sides of the scalp. Tight buns thin the sides and back. Cornrows and braids cause loss between the rows where tension concentrates. Hair extensions and weaves create pulling at their attachment points.
Even the sheer weight of very long hair can contribute. Traction alopecia has also been documented in Sikh men who wear tightly wrapped turbans over their scalp and beard hair. The key warning sign is soreness or tenderness along the hairline or wherever your style pulls tightest. Caught early, traction alopecia reverses completely once you switch to looser styles. Left too long, the repeated damage scars the follicles permanently.
Scarring Alopecia
Some conditions destroy hair follicles entirely, replacing them with scar tissue and causing permanent bald patches. One of the more well-known is lichen planopilaris, an inflammatory condition that targets the scalp. It causes red, thick, or scaly patches along with pain, itching, or a burning sensation. Over time, the inflammation scars the follicles shut.
Lichen planopilaris shows up in three distinct patterns. The classic form produces scattered bald patches across the scalp. A variant called frontal fibrosing alopecia causes the hairline near the forehead to slowly recede, sometimes taking eyebrows and eyelashes with it. A third, rarer form combines scalp patches with hair thinning in the armpits and groin, along with rough bumps around follicles on the body.
What makes scarring alopecia different from other causes is permanence. Once a follicle is replaced by scar tissue, no treatment can revive it. The goal of treatment is to stop the inflammation before more follicles are lost, which is why early diagnosis matters.
Trichotillomania
Trichotillomania is a hair-pulling disorder in which a person repeatedly pulls out their own hair, often without fully realizing they’re doing it. It produces patchy bald spots, but the patches look different from other causes. Instead of smooth, well-defined circles, the patches tend to be irregular in shape with hairs of varying lengths. You’ll see broken stubs mixed with longer strands because the pulling is inconsistent.
The scalp is the most common site, but some people pull from eyebrows, eyelashes, or other body areas. Trichotillomania often begins in adolescence and can be triggered or worsened by anxiety, boredom, or stress. It responds well to behavioral therapy, particularly a technique called habit reversal training that helps people recognize their pulling triggers and substitute alternative actions.
Less Common Causes
Secondary syphilis can produce a distinctive “moth-eaten” pattern of hair loss: multiple irregular, poorly defined patches scattered across the back and sides of the scalp. Unlike the clean, round patches of alopecia areata, moth-eaten alopecia looks ragged and uneven. This pattern is considered so specific to syphilis that it’s essentially diagnostic on its own. It results from the syphilis-causing bacteria triggering an immune response within hair follicles. The hair loss is not permanent and resolves with antibiotic treatment of the underlying infection.
Thyroid disorders, iron deficiency, and other nutritional shortfalls more commonly cause diffuse thinning across the whole scalp rather than distinct patches, but in some cases they can contribute to patchier patterns, particularly when they overlap with other conditions.
How Doctors Identify the Cause
There’s no single routine test for patchy hair loss. Diagnosis starts with what the patches look like, where they are, and how they developed. Smooth, round patches with no scaling point toward alopecia areata. Scaly, itchy patches suggest fungal infection. Patches along the hairline in someone who wears tight braids strongly suggest traction alopecia. Scarred, shiny skin within the patch raises concern for scarring alopecia.
When the cause isn’t obvious from appearance alone, blood work can help rule out contributing factors. A complete blood count, thyroid hormone levels, and iron studies are the most commonly ordered tests. For suspected fungal infections, a scalp scraping examined under a microscope or sent for culture confirms the diagnosis. In cases where scarring alopecia is suspected, a small scalp biopsy may be needed to examine the follicles directly and determine the specific type of inflammation involved.
The most important thing to pay attention to is how the patch looks and feels. A smooth, painless circle is a very different situation from a red, scaly, tender one, and that distinction shapes everything about how it gets treated and what to expect.