Alopecia is the medical term for hair loss, and it comes in many forms. The two broadest categories are non-scarring alopecia, where hair follicles stay intact and regrowth is possible, and scarring alopecia, where follicles are permanently destroyed. Within those categories, there are several distinct types, each with different causes, patterns, and outcomes.
Non-Scarring vs. Scarring Alopecia
Every type of hair loss falls into one of these two groups, and the distinction matters because it determines whether lost hair can come back. In non-scarring alopecia, the hair follicle is preserved even though it may stop producing visible hair for a while. In scarring (cicatricial) alopecia, inflammation destroys the follicle and replaces it with scar tissue. Once that happens, no treatment can restore growth in those spots without surgical intervention.
Non-scarring types can be further divided into patchy hair loss, where discrete bald spots appear, and diffuse hair loss, where thinning spreads more evenly across the scalp. Scarring types tend to leave skin that looks shiny, pale, or smooth where follicle openings used to be.
Androgenetic Alopecia (Pattern Hair Loss)
This is the most common type of hair loss in both men and women. It’s driven by a hormone called DHT, a byproduct of testosterone that binds to receptors in hair follicles and gradually shrinks them. Over time, affected follicles produce thinner, shorter, lighter hairs until they stop producing visible hair altogether. This process is called miniaturization.
In men, it typically starts with a receding hairline at the temples and thinning at the crown. Doctors classify male pattern hair loss on the 7-stage Hamilton-Norwood scale, ranging from minimal recession to near-total loss on top. In women, the pattern is different: hair thins diffusely across the top of the scalp while the frontal hairline usually stays intact. Female pattern hair loss is graded on the 3-grade Ludwig scale. Both versions are progressive without treatment, though the rate varies enormously from person to person.
Alopecia Areata
Alopecia areata is an autoimmune condition in which the immune system mistakenly attacks hair follicles, shutting down growth. It affects roughly 2% of the global population, with a lifetime risk between 1.7% and 2.1%. Hair typically falls out in small, round, coin-sized patches on the scalp, though it can appear in the beard or elsewhere on the body.
There are two more extensive variants. Alopecia totalis involves complete loss of all scalp hair, while alopecia universalis means loss of hair across the entire body, including eyebrows, eyelashes, and body hair. Because the follicles aren’t destroyed, regrowth is possible at any stage, though the condition is unpredictable and often cycles between remission and relapse.
Treatment options have expanded significantly in recent years. Since 2022, three JAK inhibitor medications have received FDA approval specifically for severe alopecia areata. In clinical trials, roughly one-third of participants with extensive hair loss achieved 80% or more scalp coverage after several months of treatment. With two years of continuous use, that number climbed to 90% in one trial. These are daily oral medications, and they’re available for adults, with one option also approved for adolescents 12 and older.
Telogen Effluvium
At any given time, 5% to 15% of the hair on your scalp is in its resting (telogen) phase. In telogen effluvium, a physiological shock pushes a much larger percentage of follicles into that resting phase simultaneously. About two to three months later, those hairs fall out, often by the handful. Because there’s a delay between the trigger and the shedding, people frequently don’t connect the two events.
Common triggers include high fevers, severe infections, major surgery, childbirth, thyroid dysfunction (especially an underactive thyroid), stopping hormonal birth control, crash dieting, low protein intake, and chronic iron deficiency. Studies have found that people with hair loss tend to have lower ferritin levels, a marker of iron stores. Certain medications, including blood thinners and beta blockers, can also trigger it.
The good news is that telogen effluvium is almost always temporary. Once the trigger is resolved, normal hair cycling resumes and lost density returns over several months.
Anagen Effluvium
While telogen effluvium involves hair falling out after it enters the resting phase, anagen effluvium happens when something stops actively growing hair cells from dividing. These cells, located at the base of each follicle, are among the fastest-dividing cells in the body, which makes them vulnerable to chemotherapy drugs and radiation. The hair shaft becomes thin and brittle, then breaks off near the scalp and falls out rapidly, sometimes within days or weeks of treatment.
Hair typically starts growing back one to three months after the trigger stops. Most people see full regrowth within three to six months, though it can take up to a year. The new hair sometimes grows back with a different texture or color initially, a common but usually temporary change.
Traction Alopecia
Traction alopecia results from repeated physical pulling on the hair. Tight ponytails, braids, cornrows, hair extensions, and heavy hair accessories can all cause it. The hair loss typically appears along the hairline or wherever tension is greatest.
In its early stages, traction alopecia is completely reversible. Remove the source of tension, and follicles recover. But chronic, long-term pulling can permanently damage follicles and cause scarring. If you’ve stopped the offending hairstyle and see no improvement after six to nine months, the affected follicles may be transitioning toward permanent loss. Skin that looks shiny or scarred in the thinning area is another warning sign that the damage has become irreversible.
Frontal Fibrosing Alopecia
Frontal fibrosing alopecia (FFA) is a type of scarring hair loss that primarily affects postmenopausal women, most often after age 50. Women of African descent tend to develop symptoms earlier, sometimes in their early 40s, and cases have been reported in women as young as 21. Men rarely develop it.
The hallmark symptom is a slowly receding hairline along the front and sides of the scalp. But eyebrow loss is often the first noticeable sign, affecting 80% to 90% of women with FFA. Hair can also thin or disappear from eyelashes, arms, legs, underarms, and the pubic area. The skin left behind may look pale, shiny, or scarred. Other symptoms can include itching or pain on the scalp, visible forehead veins (as the hairline recedes), facial hyperpigmentation, and small bumps near the hairline that resemble pimples.
FFA is a subtype of lichen planopilaris, a condition in which inflammation targets the scalp and hair follicles. Because it causes scarring, hair lost to FFA does not grow back on its own.
Other Scarring Alopecias
Beyond frontal fibrosing alopecia, other forms of scarring hair loss include classic lichen planopilaris, which causes scattered bald patches with scarring across the scalp, and a rarer variant called Lassueur-Graham-Little-Piccardi syndrome, which combines scalp scarring with hair thinning in the armpits and groin and rough bumps around hair follicles.
Central centrifugal cicatricial alopecia (CCCA) is another scarring type that most commonly affects women of African descent. It begins at the crown and spreads outward in a circular pattern. Discoid lupus can also cause scarring hair loss when lupus-related skin lesions develop on the scalp. In all scarring alopecias, early treatment is critical because the goal is to stop inflammation and preserve remaining follicles. Hair that’s already been lost to scarring won’t return.
How Types Are Identified
Dermatologists distinguish between types of alopecia based on a combination of the pattern of loss (patchy, diffuse, or along the hairline), whether the scalp looks normal or shows signs of scarring, and sometimes a scalp biopsy. A magnified scalp exam, called trichoscopy, can reveal whether follicle openings are still visible, which is the key marker separating non-scarring from scarring types. Blood tests for thyroid function, iron levels, and hormones may also be ordered when the cause isn’t obvious from the pattern alone.