A bald spot on your head usually signals one of a handful of conditions, and the most likely culprit depends on the spot’s shape, location, how fast it appeared, and whether the surrounding skin looks normal or inflamed. The most common causes are alopecia areata (an autoimmune attack on hair follicles), androgenetic alopecia (hormone-driven pattern thinning), fungal infections, and traction from tight hairstyles. Less common but worth ruling out are scarring conditions that can destroy follicles permanently. Figuring out which category your bald spot falls into matters because some causes reverse on their own, some need treatment to prevent permanent loss, and a few are red flags for something going on elsewhere in your body.
Alopecia Areata
If your bald spot is round or oval, smooth, and appeared over a few weeks with no redness, scaling, or pain, the most likely explanation is alopecia areata. This is an autoimmune condition in which your immune system mistakes hair follicles for a threat and attacks them. The hair follicle normally operates as a kind of protected zone where the immune system leaves it alone, but in alopecia areata that protection collapses. When it does, immune cells swarm the base of the follicle and shut down hair production.1PubMed. Hair follicle immune privilege and its collapse in alopecia areata The follicles are not destroyed, which is why hair can grow back, sometimes spontaneously, sometimes with treatment.
A single coin-sized patch is the most recognizable form, but alopecia areata can also produce multiple patches, or in rarer cases progress to affect the entire scalp or body. What triggers the immune system to turn on hair follicles is still not fully understood, but emotional stress appears to play a role. Research has focused on stress hormones and neuropeptides released during psychological distress that may help set off the autoimmune cascade.2PubMed Central. Psychological Stress-Induced Pathogenesis of Alopecia Areata: Autoimmune and Apoptotic Pathways Some evidence also points to viral infections and parasitic factors as possible contributors, though the condition is considered multifactorial, shaped by a combination of genetic predisposition, immune dysfunction, and environmental triggers.3RECIMA21 – Revista CientÃfica Multidisciplinar – ISSN 2675-6218. A RELAÇÃO ENTRE ALOPECIA AREATA E FATORES VIRAIS, PARASITAS E GATILHOS EMOCIONAIS
The scalp microbiome may also be involved. In people with alopecia areata, research has found that the community of microorganisms living on the scalp is significantly different from that of healthy controls. Those with more severe hair loss tend to harbor higher levels of inflammatory bacteria, and these microbial shifts correlate with elevated inflammatory markers throughout the body.4PubMed Central. Association Between Scalp Microbiota Imbalance, Disease Severity, and Systemic Inflammatory Markers in Alopecia Areata Whether the microbial changes cause the condition, result from it, or simply make it worse is still being worked out.
Androgenetic Alopecia (Pattern Hair Loss)
This is the most common cause of progressive hair thinning worldwide, and while it typically presents as gradual diffuse thinning rather than a sudden bald patch, the loss often concentrates in specific zones that can look like a distinct bald spot, particularly at the crown (vertex) of the scalp. In men, the process usually starts at the temples and crown. In women, it tends to present as widening of the central part.
The driver is dihydrotestosterone (DHT), a potent form of testosterone created when an enzyme in hair follicles converts circulating testosterone. DHT binds to receptors inside follicle cells and gradually causes the follicles to shrink, producing thinner and shorter hairs with each cycle until the follicle effectively stops producing visible hair. Men who lack the enzyme that makes DHT do not develop this type of hair loss regardless of their testosterone levels, which confirmed DHT’s central role.5Anais Brasileiros de Dermatologia. Male androgenetic alopecia
But the story is more complicated than just DHT shrinking follicles. Research suggests that DHT also contributes to thickening and scarring of the tissue surrounding follicles, and this physical remodeling restricts the space, oxygen, and nutrients available to the follicle.6PubMed. A hypothetical pathogenesis model for androgenic alopecia: clarifying the dihydrotestosterone paradox and rate-limiting recovery factors Biopsies of balding scalp consistently show inflammatory immune cells clustered around follicles and measurable thickening of the tissue sheath that surrounds them, even in areas where the hair is just beginning to thin.7PubMed. Characterization of inflammatory infiltrates in male pattern alopecia: implications for pathogenesis This inflammation component has practical treatment implications: a study found that combining standard DHT-blocking therapy with anti-inflammatory agents led to better results than DHT blockade alone, with roughly two-thirds of patients showing improvement.8PubMed Central. Perifollicular Inflammation and Fibrosis in Androgenetic Alopecia: Implications for Diagnosis and Treatment – A Comparative Histopathologic and Clinical Study with Normal-Appearing Scalp
Fungal Infections
A bald spot that looks red, scaly, or crusty, especially in a child, often turns out to be tinea capitis, a fungal infection of the scalp. The fungus invades the hair shaft itself, causing hairs to break off at or just below the skin surface, leaving patchy areas that look bald. You might notice small black dots where hairs have snapped off. The surrounding skin can be itchy, inflamed, and flaky. Tinea capitis is much more common in children than in adults, though adults can develop it too, sometimes presenting as diffuse thinning that does not look like the classic patchy infection.9PubMed Central. Tinea Capitis Presenting as Diffuse Hair Loss and Significance of Trichoscopy: Four Case Reports
Tinea capitis is contagious and can spread through shared combs, hats, pillowcases, or direct scalp-to-scalp contact. It requires oral antifungal medication because topical creams cannot penetrate the hair shaft where the fungus lives. The good news is that once the infection clears, hair almost always grows back fully because the follicles are not permanently damaged.
Traction Alopecia
If your bald spot sits along your hairline, at the temples, or wherever your hair is pulled tightest, the cause may be traction alopecia. This is hair loss from prolonged physical tension on the follicles. Tight ponytails, braids, cornrows, weaves, extensions, buns, and the habitual use of chemical relaxers all increase risk. The condition affects about a third of women of African descent who wear traumatic hairstyling over long periods, though it can develop in anyone who regularly pulls hair taut, including athletes, dancers, and people who wear tight headgear.10PubMed Central. Traction alopecia: the root of the problem
Early on, you may notice redness around follicles, small pustules, tenderness, and broken hairs. At this stage the condition is reversible if you release the tension. But if the pulling continues, the follicles eventually scar over, and once that happens the loss becomes permanent.11PubMed Central. Traction Alopecia: Clinical and Cultural Patterns The key practical takeaway is timing. If you catch it early and change your hairstyle, the hair comes back. If you wait until the skin feels smooth and shiny with no visible follicle openings, you have likely crossed into permanent territory.
Trichotillomania
Trichotillomania is a hair-pulling disorder in which a person repeatedly pulls out their own hair, often without fully realizing they are doing it. The resulting bald patches tend to have an irregular shape and contain hairs broken at many different lengths, which looks quite different from the smooth, uniform patches of alopecia areata. Under magnification, dermatologists see characteristic signs like split ends on short stubby hairs, coiled hairs, V-shaped broken hairs, and tiny hemorrhages at follicle openings.12PubMed Central. Trichoscopy in Trichotillomania: A Useful Diagnostic Tool Other distinctive markers include what clinicians call “flame hairs” (thin, wavy remnants) and “tulip hairs” (dark tips shaped like flower buds).13Acta Dermato-Venereologica. New Trichoscopy Findings in Trichotillomania: Flame Hairs, V-sign, Hook Hairs, Hair Powder, Tulip Hairs
Trichotillomania is classified as a body-focused repetitive behavior and is more common in adolescents and young adults. People often feel embarrassed and may not mention the pulling to a doctor, which means it is frequently underdiagnosed. The hair pulling can be focused (the person is aware of doing it and may feel rising tension beforehand) or automatic (done while reading, watching TV, or concentrating on something else). Treatment typically involves behavioral therapy, sometimes combined with medication. Because the follicles are mechanically damaged rather than attacked by the immune system, hair regrowth is usually possible once the pulling stops, though prolonged pulling over years can eventually cause scarring.
Scarring Alopecias
Some conditions destroy the follicle entirely and replace it with scar tissue, making the hair loss permanent. These are called cicatricial or scarring alopecias, and they account for a smaller share of bald spots overall, but they are the most urgent to diagnose because early treatment can save the remaining follicles.
Folliculitis decalvans is one form. It presents as pustules and crusting around hair follicles, often at the crown, and causes progressive scarring. It accounts for roughly 10% of primary scarring alopecia cases.14PubMed Central. Successful Management of Folliculitis Decalvans Central centrifugal cicatricial alopecia (CCCA) is another, most commonly affecting women of African descent. It typically begins at the crown and spreads outward in a centrifugal pattern. The underlying process involves inflammatory cells targeting the upper portion of the follicle, premature breakdown of the inner root sheath, and eventual replacement by fibrous tissue. Genetic factors appear to play a role, with hair-care practices involving chemicals and traction acting as aggravating factors.15PubMed. Central Centrifugal Cicatricial Alopecia: New Insights and a Call for Action
Lichen planopilaris, another lymphocytic scarring alopecia, involves immune-mediated destruction of the follicle. The immune protection that normally shields hair follicles collapses, similar to what happens in alopecia areata, but the outcome is scarring rather than temporary dormancy.16PubMed Central. Immune Privilege Collapse and Alopecia Development: Is Stress a Factor Discoid lupus erythematosus and a deeper variant called lupus panniculitis can also produce scarring patches on the scalp.17PubMed. Hair and Scalp Changes in Cutaneous and Systemic Lupus Erythematosus Scarring alopecias share a common red flag: the skin in the bald area looks shiny, pale, and lacks visible follicle openings. If your bald spot matches that description, see a dermatologist sooner rather than later, because once a follicle is replaced by scar tissue, no treatment brings it back.
Thyroid Problems and Nutritional Gaps
Sometimes a bald spot or thinning area is a sign that something metabolic is off. Thyroid hormones regulate how quickly cells grow and turn over, and the skin and hair follicles are major targets. Both an overactive and underactive thyroid can cause widespread hair shedding, and drug-induced thyroid disruption can do the same.18PubMed Central. Impact of Thyroid Dysfunction on Hair Disorders Thyroid-related hair loss typically presents as diffuse thinning rather than a sharply defined patch, but in some cases it can be patchy enough to look like a bald spot.
Nutritional deficiencies get a lot of attention as causes of hair loss, particularly iron and zinc. The actual evidence, though, suggests the role of these nutrients in isolated bald spots is smaller than popular health content implies. A cross-sectional study found that people with hair loss had slightly lower zinc, ferritin, and hemoglobin levels than controls, but both groups’ values were within normal range, and the differences were small enough to be of limited clinical relevance.19PubMed Central. Hair Loss and Zinc Deficiency: A Cross-Sectional Study This does not mean nutrition never matters for hair, but it does mean that if you are eating a reasonably balanced diet, a zinc supplement probably will not fix a bald spot. Severe deficiencies, on the other hand, particularly from malabsorption conditions, restrictive diets, or heavy menstrual bleeding, can genuinely contribute to hair loss and are worth screening for with a simple blood test.
Pressure-Induced Hair Loss
A cause that often surprises people: sustained pressure on one area of the scalp can kill off follicles. This typically happens during long surgeries, extended stays in intensive care, or any situation where your head rests in one position for hours without being moved. The pressure compresses the tiny blood vessels in the scalp, cutting off blood flow to the follicles in that area. Under anesthesia, you lack the normal reflex to shift your head when the pressure becomes uncomfortable, so the ischemia can continue unchecked for the entire duration of a procedure.20PubMed Central. Postoperative Pressure-Induced Alopecia and Perioperative Care: A Case Report
Pressure alopecia typically shows up days to weeks after the event. You notice a bald patch at the back or side of the head, exactly where your head was resting. The loss can be temporary or permanent depending on how severe the blood-flow interruption was. It falls into a broader category of scarring and non-scarring alopecias that occur after capillary obstruction at bony prominences of the skull.21PubMed. Pressure alopecias: A review If you recently had a long surgery and woke up with a sore spot on your scalp that later became a bald patch, this is almost certainly what happened. Most cases in which the damage was limited to the hair-cycle disruption (rather than full tissue death) do recover over months.
Radiation Therapy
People undergoing radiation treatment to the head for brain tumors or other cancers frequently develop hair loss in the irradiated zone. A prospective study found that the vast majority of patients receiving cranial radiation experienced some degree of alopecia. Transient hair loss occurred at relatively moderate doses, while permanent loss required higher exposure. The dose thresholds differed depending on whether you measured across the whole scalp or just at the spot where hair fell out; locally, permanent alopecia was associated with around 50 Gy at the affected area.22PLOS ONE. Scalp dose analysis for transient and permanent alopecia following conventional cranial irradiation using Image Guided Radiotherapy (IGRT): A prospective study Modern radiation planning techniques aim to limit unnecessary scalp exposure, but some degree of hair loss in the treatment field is often unavoidable. When the dose stays below the permanent-damage threshold, regrowth typically begins a few months after treatment ends, though the returning hair may differ in texture or color.
Congenital Triangular Alopecia
Not every bald spot is acquired. Congenital triangular alopecia is a benign condition that produces a triangular or oval-shaped patch of hair loss, usually in the frontotemporal area (the region between the forehead and temple). It can be present from birth or appear in early childhood, and it does not grow, change, or cause any symptoms. The follicles in the affected area produce only fine vellus hairs rather than normal terminal hairs.23PubMed Central. Congenital Triangular Alopecia Because it is stable and harmless, it is easily mistaken for alopecia areata, but the two behave very differently: alopecia areata patches fluctuate and may regrow on their own, while congenital triangular alopecia stays the same throughout life.24PubMed Central. Congenital Triangular Alopecia: A Case of Effective Response with 5% Topical Minoxidil in a Male Adolescent The condition is rare and does not require treatment, though some people pursue topical minoxidil for cosmetic reasons.
Rare Inflammatory Causes
A handful of uncommon conditions can mimic more typical bald spots and trip up even experienced clinicians. Alopecia mucinosa (also called follicular mucinosis) is a rare inflammatory condition in which mucin, a gel-like substance, accumulates inside hair follicles and sebaceous glands, disrupting normal hair growth. It presents as raised, follicular bumps that may or may not sit on a red, scaly plaque, with clear hair loss in the affected area.25Journal of Skin and Sexually Transmitted Diseases. Alopecia mucinosa: A case report Diagnosis requires a biopsy showing mucin deposits in the follicle tissue, and the condition needs to be distinguished from other forms of alopecia because in some adults it can be associated with lymphoma.26PubMed. Clinical and histopathologic spectrum of alopecia mucinosa/follicular mucinosis and its natural history in children In children, alopecia mucinosa tends to resolve on its own and carries no such association.
How to Tell the Causes Apart
When you are staring at a bald spot in the mirror, a few features can help you narrow down what you are dealing with before you see a doctor:
- Smooth and round: A clean, circular patch with no redness or scaling points toward alopecia areata. Look for “exclamation mark” hairs at the edges, which are short hairs that taper toward the scalp.
- Red, scaly, or crusty: Scaling, redness, or broken-off hairs with black dots suggest tinea capitis or another inflammatory condition. If you see pus around follicle openings, scarring alopecias like folliculitis decalvans enter the picture.
- Along the hairline: Loss concentrated where hair is pulled tightest, particularly along the frontal hairline or at the temples, suggests traction alopecia.
- Irregular shape, mixed hair lengths: A patch with a bizarre outline and hairs broken at many different lengths raises the possibility of trichotillomania.
- Gradual thinning at the crown or part: Progressive loss in the classic male or female pattern suggests androgenetic alopecia.
- Shiny, pale skin with no follicle openings: This is the hallmark of scarring alopecia. The follicles are gone, and the spot will not regrow without intervention, if at all.
A dermatologist can often narrow the diagnosis just by looking at the spot under magnification with a dermatoscope. Different conditions produce distinctive patterns visible at the follicle level, such as yellow dots, black dots, broken hairs, or the absence of follicular openings.27PubMed Central. Trichoscopic Patterns of Nonscarring Alopecia’s – Section: Abstract When the visual pattern is not definitive, a small scalp biopsy and sometimes blood work (thyroid levels, iron studies, inflammatory markers) complete the picture. Self-diagnosing bald spots from photos online is unreliable because many conditions overlap in appearance, and the distinction between scarring and non-scarring hair loss, which determines how urgently you need treatment, requires a trained eye or a biopsy to confirm.
The Scalp Microbiome Connection
An emerging area of research is the relationship between the community of bacteria, fungi, and other microorganisms living on your scalp and the health of your hair follicles. Disrupted microbial balance, or dysbiosis, has been linked not only to alopecia areata but also to androgenetic alopecia, where altered microbial compositions and localized inflammation may accelerate follicular miniaturization.28The Microbe. Unlocking the secrets of the hair microbiome: From scalp health to therapeutic advances This does not mean a probiotic shampoo will cure your bald spot. The science is still in its early stages, and no scalp microbiome intervention has been validated in clinical trials for hair regrowth. But it does suggest that chronic scalp inflammation, whether driven by microbes, autoimmunity, or hormones, is a shared thread running through many different types of hair loss, and future treatments may target the microbial angle alongside the hormonal or immune ones.