Alopecia is the medical term for hair loss, and it covers a wide range of conditions, from small bald patches that regrow on their own to permanent loss across the entire body. Some forms are extremely common: pattern hair loss affects more than half of men over 50 and up to 75% of women over 65. Others, like the autoimmune form called alopecia areata, carry a lifetime risk of about 2% and can strike at any age.
Understanding which type of alopecia you’re dealing with matters because the cause, outlook, and treatment options differ dramatically between them.
The Main Types of Alopecia
Hair loss falls into three broad categories: pattern hair loss, autoimmune hair loss, and scarring hair loss. Each one damages hair in a fundamentally different way.
Pattern Hair Loss (Androgenetic Alopecia)
This is the most common form overall. In men, it typically shows up as a receding hairline and thinning at the crown, often starting in the late teens or twenties. In women, it usually appears as diffuse thinning over the top of the scalp, becoming more noticeable after menopause. The hair follicles aren’t destroyed. Instead, they gradually shrink, producing thinner and shorter strands with each cycle until the hairs are nearly invisible. That shrinking process is driven by a hormone called DHT, a potent form of testosterone that binds to receptors inside the follicle and disrupts the signals that keep hair growing.
Alopecia Areata
Alopecia areata is an autoimmune condition. It typically appears as smooth, round patches of sudden hair loss on the scalp, though it can affect any area of the body. A telltale sign during active episodes is “exclamation-mark hairs,” short broken strands that are narrower at the base than at the tip, visible at the edges of bald patches.
Most people with alopecia areata have patchy hair loss that comes and goes. About 10% progress to more severe forms: alopecia totalis (complete loss of scalp hair) or alopecia universalis (complete loss of all body hair, including eyebrows and eyelashes). There are also less common patterns, such as ophiasis, where hair loss follows a band around the back and sides of the head.
Scarring (Cicatricial) Alopecia
In scarring alopecia, the hair follicle is permanently destroyed and replaced by scar tissue. The affected skin looks smooth and shiny, and the pores where hair once grew disappear entirely. Unlike pattern hair loss or alopecia areata, the follicles cannot regenerate, so regrowth isn’t possible in scarred areas. Several distinct conditions fall under this umbrella, including lichen planopilaris and frontal fibrosing alopecia. Burns, radiation, and trauma can also cause permanent scarring hair loss.
Telogen Effluvium
This is a temporary form of diffuse shedding triggered by a shock to the system: major illness, surgery, childbirth, rapid weight loss, or severe stress. A large number of hairs shift into the resting phase at once and fall out two to three months later. It can be alarming because the volume of shedding is dramatic, but the follicles aren’t damaged. Hair typically regrows within several months once the trigger resolves.
What Causes Each Type
Pattern hair loss is driven by genetics and hormones. The enzyme that converts testosterone into DHT is especially active in the follicles at the front and top of the scalp. DHT binds to those follicles with much higher affinity than regular testosterone, shortening the growth phase and extending the resting phase. Over time, each cycle produces a finer, shorter hair until the follicle essentially goes dormant. People with pattern hair loss tend to have higher concentrations of hormone receptors in the affected areas, which is why the sides and back of the head are usually spared.
Alopecia areata is caused by immune cells attacking hair follicles. Specifically, a type of killer T-cell infiltrates the follicle and releases inflammatory signals that collapse the follicle’s natural immune protection. This creates a self-reinforcing loop: the inflammation attracts more immune cells, which cause more damage. The trigger for this immune attack isn’t fully understood, but genetics play a role, and it’s more common in people with other autoimmune conditions like thyroid disease or vitiligo.
Nutrient deficiencies can contribute to hair loss as well, particularly in telogen effluvium. People with diffuse hair loss tend to have significantly lower iron stores and vitamin D levels compared to people without hair loss. In one study, nearly 80% of patients with diffuse hair loss had low vitamin D, and about 20% had low iron (ferritin). Low zinc has also been linked to both telogen effluvium and alopecia areata, though it’s less common, affecting roughly 10% of patients with hair loss.
How Alopecia Is Diagnosed
A dermatologist can usually identify the type of hair loss through a physical exam and your medical history. The pattern, speed of onset, and appearance of the scalp all provide important clues. Smooth, round bald patches with visible pores suggest alopecia areata. Shiny, poreless patches point to scarring alopecia. Gradual thinning at the crown or temples is the hallmark of pattern hair loss.
A simple hair pull test is one of the first things a doctor may do. They’ll gently slide their fingers along a small section of hair in several areas of your scalp. Pulling out more than six hairs indicates active shedding. Fewer than three is considered normal.
When the diagnosis isn’t clear, a small scalp biopsy can help. The dermatologist takes a tiny plug of skin, typically 4 millimeters wide, from the leading edge of a hair loss patch, where there’s still a mix of affected and unaffected follicles. Examining the tissue under a microscope reveals whether follicles are miniaturized, inflamed, or replaced by scar tissue.
Blood work may be ordered to check for contributing factors like iron deficiency, thyroid problems, vitamin D levels, or hormonal imbalances.
Treatment for Pattern Hair Loss
The two most established treatments for androgenetic alopecia work by either stimulating follicles or blocking DHT. Minoxidil (available over the counter as a topical liquid or foam, and increasingly prescribed in oral form) improves blood flow to follicles and extends the growth phase. Finasteride (a prescription pill) blocks the enzyme that converts testosterone into DHT, slowing or stopping the miniaturization process.
When used together, these two treatments produce meaningful results. In a large retrospective analysis, over 92% of patients maintained or improved their hair density after 12 months on combined oral therapy, and more than 57% showed noticeable improvement. These aren’t cures; stopping treatment typically means the hair loss resumes. But for many people, they effectively hold the line or partially reverse thinning.
Treatment for Alopecia Areata
Alopecia areata treatment has changed significantly in recent years. Mild, patchy cases often regrow on their own or with steroid injections into the affected patches. But for moderate to severe cases, a new class of drugs called JAK inhibitors has become the standard of care.
Three JAK inhibitors are now FDA-approved for alopecia areata. The first, baricitinib, was approved in 2022 and achieved 80% or greater scalp hair coverage in 35 to 40% of patients by 36 weeks. Ritlecitinib followed in 2023 (approved for ages 12 and up), with about 32% of patients reaching that same level of regrowth by 24 weeks. Deuruxolitinib, approved in 2024, showed similar results, with 41% of patients achieving significant coverage by 24 weeks.
These drugs work by blocking the inflammatory signaling pathways that drive the immune attack on hair follicles. They don’t cure the underlying autoimmune tendency, so hair loss may return if the medication is stopped, but they represent a major advance for people with extensive alopecia areata who previously had few effective options.
Scarring Alopecia and Irreversible Loss
With scarring alopecia, the goal of treatment shifts from regrowth to stopping further damage. Once a follicle is destroyed and replaced by fibrous tissue, no medication can bring it back. Treatment focuses on reducing the inflammation that’s destroying follicles at the active edges of the patches, typically with anti-inflammatory medications or immune-suppressing therapies.
For areas already scarred, hair transplantation is sometimes an option if the disease has been stable and inactive for a sufficient period. Early diagnosis is critical because the window to save follicles closes once scarring is complete.
The Role of Nutrition
While nutrient deficiencies alone rarely cause dramatic hair loss, they can worsen shedding or slow regrowth. Iron is the most studied nutrient in this context. Women with chronic diffuse hair loss frequently have low ferritin (the stored form of iron) even when they aren’t technically anemic. In studies comparing hair loss patients to healthy controls, average ferritin levels were nearly half as high in the hair loss group.
Vitamin D deficiency is even more common among people with hair loss. Vitamin D plays a role in the hair follicle’s growth cycle, and levels below 20 ng/ml (considered insufficient) are found in the majority of patients with diffuse shedding. Zinc deficiency, while less prevalent, has been found at higher rates in people with both telogen effluvium and alopecia areata compared to the general population.
Correcting these deficiencies won’t reverse pattern hair loss or cure an autoimmune condition, but it can remove one barrier to healthy hair growth and may help other treatments work more effectively.
Emotional Impact and What to Expect
Hair loss affects more than appearance. Alopecia areata in particular can be unpredictable, with cycles of loss and regrowth that make it difficult to plan or feel in control. Studies consistently rank it among the autoimmune conditions with the greatest impact on quality of life, especially in younger adults.
The outlook depends heavily on the type. Pattern hair loss is progressive but manageable with consistent treatment. Alopecia areata is unpredictable: many people with mild cases experience full regrowth, while those who progress to totalis or universalis face longer, more uncertain timelines. Scarring alopecia requires early intervention to preserve what remains. In all cases, working with a dermatologist who can identify the specific type and tailor treatment accordingly gives you the best chance of a good outcome.