Hair loss is one of the most common and least understood medical conditions affecting adults. By age fifty, roughly half of men and around a quarter of women will experience clinically significant thinning. Most will respond by trying whatever product happens to appear in their social-media feed — and most will be disappointed, because the right treatment depends entirely on what's actually causing the loss in the first place.
This article is the foundation. It covers how hair actually grows, the main categories of hair loss, what drives the most common type, when it's time to involve a doctor, and what the treatment landscape actually looks like in 2025. If you read one article on this topic, make it this one.
The Hair Growth Cycle
Every hair on your body cycles through four distinct phases, and almost every form of hair loss involves a disruption to one of them.
The anagen phase is active growth. This is when the follicle is producing the hair shaft, the hair is anchored to the scalp, and visible length is being added — about a centimeter per month. Anagen typically lasts two to seven years per follicle, and the duration is genetically determined. The longer your anagen phase, the longer your hair can grow before it sheds.1
The catagen phase is a brief transitional period — about two to three weeks — during which the follicle detaches from its blood supply and stops producing hair. This is followed by the telogen phase, a resting period of about three months during which the hair remains in the follicle but is no longer growing. Finally, the exogen phase is the actual shedding event, after which the follicle re-enters anagen and starts a new cycle.
At any given moment, roughly 85% of your scalp hair is in anagen, 1–2% is in catagen, and 10–15% is in telogen. Losing 50 to 100 hairs a day from telogen-to-exogen turnover is completely normal. Hair loss as a condition occurs when this balance shifts — either because the anagen phase shortens, more follicles enter telogen at once, or follicles fail to re-enter anagen at all.
The Main Types of Hair Loss
There are several distinct types of hair loss, and they require very different approaches. Understanding which one you're dealing with is the first and most consequential step in finding a treatment that works.
Androgenetic Alopecia (Male and Female Pattern Hair Loss)
By far the most common type, accounting for the vast majority of hair-loss cases in both men and women. Androgenetic alopecia (AGA) is a genetically inherited sensitivity in scalp follicles to dihydrotestosterone (DHT), a metabolite of testosterone. Over time, exposure to DHT causes follicles to miniaturize — each successive growth cycle produces a finer, shorter, less pigmented hair until the follicle effectively stops producing visible hair entirely.2
The pattern is recognizable: in men, recession at the temples and thinning at the crown, often progressing to the classic horseshoe shape. In women, diffuse thinning at the top of the scalp with the frontal hairline usually preserved.
Telogen Effluvium
A temporary form of hair loss in which a large number of follicles enter telogen at once, typically two to three months after a triggering event. Common triggers include severe illness, high fever, surgery, rapid weight loss, childbirth, emotional trauma, and certain medications. The shedding can be alarming — twice or three times normal levels — but the follicles themselves are not damaged. In most cases, the condition resolves on its own within six to nine months as the cycle normalizes.
Alopecia Areata
An autoimmune condition in which the immune system mistakenly attacks the hair follicle, causing well-defined patches of hair loss that can appear on the scalp, face, or anywhere else hair grows. In severe cases (alopecia totalis or universalis), the condition affects all scalp hair or all body hair. Treatment typically requires medical management and may involve topical or injected corticosteroids, immunotherapy, or newer JAK inhibitors.
Scarring (Cicatricial) Alopecia
A group of rare disorders in which the follicle is permanently destroyed and replaced by scar tissue. Unlike AGA or telogen effluvium, scarring alopecia is irreversible — once the follicle is gone, no treatment can restore growth from that location. Early intervention to stop the underlying inflammation is critical, which makes early diagnosis essential.
Traction Alopecia
Caused by repeated mechanical tension on the follicle — tight hairstyles like braids, ponytails, or extensions sustained over months or years. The earliest stages are reversible if tension is removed; long-standing cases can produce permanent scarring.
The Real Drivers of Androgenetic Hair Loss
Because AGA accounts for the vast majority of hair-loss cases, it deserves a closer look at its underlying biology. The condition is rarely the result of any single factor. Research over the past two decades has identified at least four overlapping mechanisms that together drive the miniaturization process.
DHT Sensitivity
The 5-alpha-reductase enzyme converts testosterone into DHT, which then binds to androgen receptors in scalp follicles. In genetically susceptible individuals, this binding shortens the anagen phase and progressively miniaturizes the follicle.3 Critically, the issue isn't necessarily that DHT levels are high — it's that the follicles in affected scalp regions are unusually sensitive to it.
Chronic Inflammation
Low-grade perifollicular inflammation is now recognized as a major contributor to AGA progression. Inflammatory cytokines disrupt the local signaling environment, accelerate follicle damage, and shorten the active growth phase. This is one reason why peptide-based approaches that address inflammation have gained traction.4
Oxidative Stress
The accumulation of reactive oxygen species in scalp tissue damages follicle stem cells and dermal papilla cells, the two populations responsible for sustaining the growth cycle. Antioxidant support — through both topical and oral pathways — is increasingly recognized as a meaningful intervention.
Reduced Microvascular Flow
Follicles are metabolically demanding tissues that depend on consistent blood supply. As the scalp ages, microvascular density tends to decline, which limits the nutrients and oxygen reaching the follicle. This is the pathway minoxidil targets, but it can also be supported through non-pharmacological means.
When To See A Doctor
Most cases of androgenetic hair loss can be addressed without a dermatologist visit, but several presentations warrant medical evaluation. Sudden, severe shedding that started without an obvious trigger; clearly defined bald patches; itching, burning, or visible scalp inflammation; hair loss accompanied by other symptoms like fatigue or weight changes; and any sign of scarring should all be evaluated. A dermatologist can perform a scalp examination, order a basic blood panel to rule out nutritional or hormonal causes, and in some cases conduct a biopsy to confirm the specific type of alopecia.
The Treatment Landscape
The treatments available in 2025 fall into roughly five categories, ranked by clinical evidence.
Prescription pharmaceuticals. Finasteride (oral) and dutasteride (oral) are FDA-approved 5-alpha-reductase inhibitors that lower systemic DHT. They work, but their side-effect profile — sexual side effects, mood changes, and rare but documented persistence after discontinuation — limits adoption.5
Topical minoxidil. The original OTC standard. Works as a vasodilator and anagen-phase extender. Requires lifelong daily use and produces irritation in a meaningful subset of users.
Peptide therapies. The newest and fastest-growing category. GHK-Cu, in particular, has emerged as a well-studied alternative with a clean side-effect profile and a multi-pathway mechanism that addresses inflammation, oxidative stress, and follicle signaling simultaneously.6
Surgical restoration. Hair transplant (FUE or FUT) is effective but expensive, irreversible, and only viable for patients with sufficient donor hair. Best considered after non-surgical options have been tried.
Lifestyle and supportive interventions. Stress management, adequate protein and micronutrient intake (iron, vitamin D, zinc, biotin), and sleep are not standalone treatments but meaningfully affect treatment response.
The Bottom Line
Hair loss is treatable, but only if you know what you're treating. Identify the type, understand the drivers, and choose a protocol matched to your specific situation. For the vast majority of cases — androgenetic alopecia — the modern protocol combines a DHT-control strategy, a scalp-signaling agent like GHK-Cu, and lifestyle support. The era of single-pill, single-spray solutions is ending. Multi-pathway approaches are where the evidence is heading.
