The inability to grow hair is most commonly called alopecia, a broad medical term covering many forms of hair loss. When hair never develops in the first place or stops growing permanently, more specific terms apply: atrichia describes a complete absence of hair growth, while hypotrichosis refers to abnormally sparse or thin hair. Which term fits depends on whether you once had hair and lost it, or whether your body never produced it normally to begin with.
Alopecia: The Umbrella Term
Alopecia is the general medical word for hair loss of any kind. It affects roughly 2% of the global population in its autoimmune form alone, and the term gets modified depending on how much hair is lost and where. Alopecia areata causes patchy, circular bald spots. Alopecia totalis means losing all or nearly all scalp hair. Alopecia universalis, the rarest form, involves complete or near-complete loss of hair across the entire body, including eyebrows, eyelashes, and body hair.
These forms exist on a spectrum. Someone might start with a small bald patch and never progress further, or the patches may expand over months until no hair remains. The key feature of alopecia areata and its variants is that the hair follicles are still alive beneath the skin. They’ve been attacked by the immune system, but they haven’t been destroyed, which is why regrowth remains possible even after years of baldness.
How Autoimmune Hair Loss Works
Alopecia areata is a T-cell mediated autoimmune disease. Hair follicles normally enjoy a kind of immune protection, a biological shield that prevents the body’s defenses from attacking them. In alopecia areata, that shield breaks down. Immune cells swarm the base of the hair follicle and force it out of its growth phase prematurely. Normally, about 80% of your scalp hairs are actively growing at any given time, with 20% in a resting phase. In people with alopecia areata, that ratio shifts dramatically, sometimes to 50:50 or worse, and hairs fall out faster than they can be replaced.
Diagnosis is usually straightforward. Doctors look for smooth, round patches of hair loss with short, tapered “exclamation mark” hairs at the edges. A scalp biopsy is rarely needed but will show immune cells clustered around the hair follicle bulbs.
Atrichia: When Hair Never Grows Back
Atrichia is different from alopecia in one critical way: the hair follicles are permanently gone or permanently nonfunctional. Atrichia congenita, the inherited form, is caused by a mutation in the hairless (HR) gene on chromosome 8. Babies with this condition are born with hair that looks normal, but it falls out within the first one to six months of life and never grows back. Eyebrows, eyelashes, and body hair may also be sparse or completely absent, though some individuals develop a few pubic or underarm hairs later.
A related condition called atrichia with papular lesions (APL) adds another visible sign: small, firm, skin-colored bumps that appear on the face, neck, arms, and trunk. These bumps are keratin cysts that form in the skin where hair follicles should be. APL is also inherited in an autosomal recessive pattern, meaning both parents must carry the gene mutation.
Doctors distinguish congenital atrichia from autoimmune alopecia universalis by the timeline. In atrichia, the hair sheds gradually in infancy without the sudden, patchy loss characteristic of autoimmune disease. There’s no inflammation visible on the scalp, and the hair simply never returns.
Scarring vs. Non-Scarring Hair Loss
One of the most important distinctions in hair loss is whether the follicle itself has been destroyed. Non-scarring alopecia, including pattern baldness and alopecia areata, leaves the follicle openings visible on the scalp. The follicles are dormant or suppressed, but they still exist and can potentially reactivate.
Scarring alopecia (also called cicatricial alopecia) is permanent. Inflammation destroys the follicle tissue, and the body replaces it with scar tissue. Once that happens, no treatment can regrow hair from those follicles. The goal of treatment shifts to stopping the scarring from spreading to healthy follicles nearby. Several autoimmune and inflammatory diseases can cause this type of permanent damage.
Systemic Diseases That Stop Hair Growth
Hair loss isn’t always a standalone condition. It frequently accompanies broader autoimmune and inflammatory diseases, and in some cases, the damage is irreversible.
Lupus is one of the most common culprits. About 50% of people with systemic lupus erythematosus experience hair loss at some point. The severity ranges from mild thinning to losing more than half the scalp’s hair. When lupus affects the skin directly in its discoid form, about one-third of cases progress to irreversible scarring alopecia. The scarring destroys the stem cells that live in the follicle’s bulge area, permanently eliminating the follicle’s ability to produce hair.
Other conditions linked to significant hair loss include dermatomyositis (scalp involvement in 63 to 82% of patients, with hair loss in up to 87%), systemic sclerosis (which can cause irreversible scarring alopecia), and rheumatoid arthritis (which triggers diffuse, non-scarring shedding). Even Sjogren’s syndrome, primarily known for dry eyes and mouth, is associated with dry, brittle hair and a form of frontal hairline recession.
How Doctors Tell These Conditions Apart
A close-up examination of the scalp using a dermatoscope (a specialized magnifying tool) reveals patterns invisible to the naked eye. In alopecia areata, doctors look for exclamation mark hairs, yellow dots in empty follicles, and short regrowing hairs. In fungal infections that mimic alopecia, they find comma-shaped or corkscrew hairs caused by fungal invasion of the hair shaft. Trichotillomania, a condition where people pull their own hair, shows hairs broken at different lengths, V-shaped pairs of snapped hairs, and sometimes small hemorrhages around follicles.
The most important distinction is whether follicular openings are still visible. If you can see the tiny pores where hair should emerge, the condition is non-scarring and potentially reversible. If the skin is smooth and the openings are gone, scarring has occurred and that hair is permanently lost.
Treatment Options for Severe Hair Loss
For autoimmune alopecia areata, treatment has changed significantly in recent years. Three medications in a class called JAK inhibitors have received FDA approval specifically for severe cases. The first, approved in June 2022, showed that 35 to 40% of patients achieved at least 80% scalp hair coverage within about nine months. A second, approved in June 2023 for patients aged 12 and older, showed increasing effectiveness over time: 45% of participants had significant regrowth after one year, rising to 61% after two years. A third was approved in July 2024.
These medications work by blocking the immune signals that attack hair follicles, essentially restoring the follicle’s immune protection. They represent the first targeted therapies for alopecia areata and are prescribed for people who have lost 50% or more of their scalp hair.
For congenital atrichia and scarring alopecia, no medication can regrow hair from destroyed or absent follicles. Treatment focuses on preventing further loss in scarring conditions, and cosmetic options like wigs and scalp prosthetics for both. Hair transplantation may help in localized scarring cases where healthy donor follicles are available elsewhere on the scalp.