Alopecia is the medical term for hair loss. It covers everything from gradual thinning on the top of your head to sudden bald patches to complete loss of hair across the entire body. The word itself dates back to Hippocrates and comes from the Greek word “alopex,” meaning fox, a reference to the patchy fur loss seen in foxes with mange. While “alopecia” is a single word, it describes a wide range of conditions with very different causes, patterns, and outcomes.
The Main Types of Alopecia
Not all hair loss works the same way. The type of alopecia you have determines what caused it, how it progresses, and whether the hair can grow back.
Androgenetic alopecia is the most common form, affecting men, women, and adolescents. This is what most people call male-pattern or female-pattern baldness. In men, it typically starts at the temples and crown. In women, hair thins more evenly across the center of the scalp while the frontal hairline stays mostly intact. It progresses slowly over years.
Alopecia areata is an autoimmune condition that causes sudden, patchy hair loss. Round, smooth bald spots appear on the scalp, and the skin underneath looks normal with no scarring or redness. It affects roughly 2% of the global population, with the heaviest burden falling on people between ages 25 and 39. About 30 to 50% of people with patchy alopecia areata see their hair grow back on its own within the first 6 to 12 months.
Alopecia totalis means complete loss of all scalp hair. Alopecia universalis goes further, involving loss of all hair on the entire body, including eyebrows, eyelashes, and body hair. Both are rare, advanced forms of alopecia areata.
Traction alopecia results from physical pulling on the hair over time. Tight braids, cornrows, ponytails, weaves, dreadlocks, and extensions can all cause it. The risk goes up when tension is combined with chemical relaxers or heat styling, which weaken the hair shaft. Ballet dancers, military personnel, and anyone who regularly wears tightly pulled hairstyles are at higher risk.
Scarring vs. Non-Scarring Hair Loss
One of the most important distinctions in alopecia is whether the hair follicle itself is destroyed. In non-scarring types like androgenetic alopecia and alopecia areata, the follicle remains intact beneath the skin. The hair may stop growing or become extremely fine, but the biological machinery is still there, which means regrowth is possible with treatment or even spontaneously.
In scarring (cicatricial) alopecia, inflammation destroys the follicle and replaces it with scar tissue. Once that happens, hair cannot regrow from that spot. Traction alopecia sits in an interesting middle ground: caught early, it’s reversible, but years of repeated tension can permanently destroy follicles and become a scarring condition.
What Causes Androgenetic Alopecia
Pattern baldness is driven by a hormone called DHT (dihydrotestosterone). An enzyme in your scalp converts testosterone into DHT, which binds to receptors in the hair follicle far more strongly than testosterone itself. People with androgenetic alopecia tend to have more of these receptors in the frontal and crown areas of the scalp, making those regions especially sensitive.
Over time, DHT disrupts the signals that tell follicle stem cells to regenerate. It shortens the growth phase of the hair cycle from years down to weeks or months, while extending the resting phase. The result is that thick, pigmented hairs are gradually replaced by finer, shorter, nearly invisible ones. This process, called miniaturization, is why thinning hair often looks wispy before it disappears entirely. Genetics determine how sensitive your follicles are to DHT, which is why pattern baldness runs in families.
How Alopecia Areata Attacks Hair Follicles
Alopecia areata is fundamentally different from pattern baldness. It’s an autoimmune condition where your immune system mistakenly targets hair follicles as though they were foreign invaders. Specific immune cells, primarily a type of white blood cell called CD8+ T cells, cluster around the base of the hair follicle and release inflammatory signals that shut down hair production.
What makes this condition persistent is a feedback loop. The attacking immune cells release a chemical signal that causes the follicle’s own cells to produce another signal, which in turn activates more immune cells, which release more of the first signal. This self-reinforcing cycle is why alopecia areata can flare unpredictably and why it sometimes expands from a single patch to widespread loss. The good news is that the follicle itself is not destroyed. The immune attack puts it into a dormant state, but if the immune assault stops, the follicle can resume producing hair.
Signs Beyond Hair Loss
Alopecia areata often announces itself with a distinctive clue: short, broken hairs that taper to a narrow point near the scalp, sometimes called exclamation mark hairs. These stubby hairs at the edges of a bald patch are a hallmark of the condition.
Nail changes are another common signal that many people overlook. Tiny pits on the nail surface, arranged in a grid-like pattern, appear in many people with alopecia areata. These pits are often so shallow they’re barely noticeable unless you look closely. Other nail changes include rough, sandpaper-like texture across the entire nail, small white spots, reddish discoloration of the half-moon at the nail base, and brittle or ridged nails. Nail involvement doesn’t always correlate with the severity of hair loss, but it can help confirm the diagnosis.
Treatment Options
Treatment depends entirely on which type of alopecia you have. For androgenetic alopecia, the goal is to block DHT or stimulate the follicle before miniaturization becomes irreversible. Topical treatments and oral medications that interfere with DHT production are the standard approach, and they work best when started early.
For alopecia areata, treatment has changed significantly in recent years. Three JAK inhibitors have received FDA approval, each targeting the inflammatory signaling loop that drives the immune attack on follicles. In clinical trials, these medications helped 32 to 41% of participants achieve at least 80% scalp hair coverage within 24 to 36 weeks, with results continuing to improve over time. One of these drugs saw 61% of participants reach that level of regrowth by the two-year mark. These medications represent a major shift for people with moderate to severe alopecia areata, who previously had limited options.
For traction alopecia, treatment is straightforward: stop the tension. Switching to looser hairstyles, avoiding chemical relaxers on stressed hair, and giving the scalp time to recover can allow follicles to resume normal growth, as long as permanent scarring hasn’t set in.