Sudden bald spot on Head Woman-tshblog

A sudden bald spot is unsettling, but it’s also a common enough concern that dermatologists see it regularly. In women, a sudden, well-defined bald patch (rather than gradual, diffuse thinning) most often points to one of two things: alopecia areata or telogen effluvium. They look different under examination and need different approaches, so getting the distinction right matters.

Alopecia areata vs. telogen effluvium

Alopecia areata is an autoimmune condition in which the immune system mistakenly attacks hair follicles, causing sudden, well-defined round or oval bald patches — often with smooth, otherwise-healthy-looking skin at the site. It can appear anywhere hair grows, including eyebrows and eyelashes.

Telogen effluvium, by contrast, typically causes diffuse thinning rather than a sharply defined patch, though in more pronounced cases it can look patch-like too. It’s triggered by significant physical or emotional stress — illness, surgery, major life stress, or nutrient deficiency — and shows up as increased daily shedding rather than a localized autoimmune attack on follicles.

A dermatologist can usually distinguish between the two through a scalp exam and a few simple tests, which matters because the treatment approach differs.

Other possible causes

Beyond the two most common causes, a sudden bald spot can also be linked to:

• Hypothyroidism or hyperthyroidism
• Nutritional deficiencies (iron, zinc, vitamin D, protein)
• Genetic factors
• High fever or recent severe illness
• Pernicious anemia
• Pregnancy and postpartum hormonal changes
• Significant physical or emotional shock

How it’s diagnosed

A dermatologist typically works through several steps to identify the cause:

1. Examining the scalp, the affected area, and the overall pattern of hair loss (well-defined patch vs. diffuse thinning).
2. Asking about daily hair loss — shedding beyond roughly 100 hairs a day can indicate an active issue worth investigating further.
3. A hair pull test, gently pulling a small section of hair to see how easily it releases and examining the hair root.
4. Assessing hair lost during washing and combing.
5. Blood tests, which commonly include a complete blood count, hormone panel, thyroid function test, and urinalysis, to identify an underlying cause like a thyroid condition or deficiency.

Treatment depends on the cause

Because the causes differ, there’s no single treatment that works for every sudden bald spot — the right approach depends on the diagnosis:

• For alopecia areata, dermatologists commonly use corticosteroid injections directly into the affected area, or topical or oral corticosteroids for more extensive cases — this requires a dermatologist’s supervision, not self-treatment.
• For telogen effluvium, treatment centers on identifying and addressing the underlying trigger; see our full guide on telogen effluvium for the details.
• Minoxidil, the only FDA-approved OTC hair-loss medication, is sometimes used alongside treatment for either condition to support regrowth — see our guide on dermatologist-recommended hair growth products for options.
• Nutrient deficiencies, if confirmed by blood testing, are addressed with targeted supplementation rather than a broad multivitamin approach — and gentle hair care (a wide-tooth wooden comb, avoiding harsh chemical treatments) helps reduce additional breakage while hair recovers.

When to see a dermatologist

Any sudden, well-defined bald patch is worth a dermatologist visit rather than guessing at the cause — the difference between alopecia areata and telogen effluvium isn’t always obvious without a proper exam, and starting the right treatment early generally gives better results than waiting.