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Types of Hair Loss
Alopecia is the medical term for hair loss, but hair loss is not a single disease. It includes many different disorders with distinct causes, patterns of progression and treatment needs. Hair loss may result from inherited susceptibility, autoimmune disease, inflammation, infection, hormonal or metabolic changes, medications, nutritional deficiencies, physical or chemical injury, abnormalities of the hair shaft and other medical conditions.
Androgenetic alopecia is the most common form of progressive hair loss and includes male pattern hair loss and female pattern hair loss. Other important types include telogen effluvium, anagen effluvium, alopecia areata, scarring alopecias, congenital hypotrichosis, hair shaft disorders, traction alopecia and hair loss associated with infectious disease.
Hair loss disorders can also be broadly distinguished by whether the follicle remains intact or is permanently destroyed. Many nonscarring forms of alopecia allow the possibility of continued growth or regrowth, while scarring alopecias can permanently destroy affected follicles. Conditions that appear similar at first can therefore have very different long term consequences, and more than one form of hair loss can occur at the same time.
The same visible complaint, whether increased shedding, diffuse thinning, patchy hair loss or breakage, can arise from very different biological processes. A person may be shedding because of telogen effluvium, experiencing progressive follicular miniaturization from androgenetic alopecia, developing autoimmune hair loss from alopecia areata or losing follicles permanently because of inflammatory scarring alopecia.
Hair loss can also occur in connection with systemic illness, thyroid and other hormonal disorders, pregnancy, nutritional deficiency, medications, chemotherapy, repeated traction, infection and damaging grooming practices. Some conditions are relatively straightforward to recognize. Others may require evaluation by a dermatologist with specific experience in hair and scalp disorders, particularly when inflammation, scarring, rapid progression or an unusual pattern is present.
Evaluation may include examination of the scalp and hair, medical history, trichoscopy, laboratory testing, fungal testing or a scalp biopsy. An accurate diagnosis matters because treatment appropriate for one form of hair loss may have little value for another, and delays can be especially important when follicles are at risk of permanent destruction.
The categories below provide a practical framework for understanding several of the major types of hair loss and hair disorders. They also illustrate one of the most important principles in hair loss treatment: before deciding how hair loss should be treated, it is essential to understand what is happening to the hair follicle and why.
Androgenetic Alopecia
Androgenetic alopecia is the most common form of progressive hair loss. Often called male pattern hair loss or female pattern hair loss, it involves gradual miniaturization of genetically susceptible hair follicles and typically develops in recognizable patterns that can differ between men and women.
Effluviums
Effluviums are hair loss conditions involving disruption of the normal hair growth cycle. Telogen effluvium causes increased shedding as more follicles enter the resting phase, while anagen effluvium results from interruption of actively growing hairs and can produce more rapid hair loss.
Alopecia Areata
Alopecia areata is an autoimmune disease in which the immune system attacks hair follicles. Hair loss may range from one or more patches to extensive loss of scalp or body hair. Because the follicles are generally not permanently destroyed, regrowth is possible, although the course of the disease can be unpredictable.
Scarring Alopecia (Cicatricial Alopecia)
Scarring alopecia, also known as cicatricial alopecia, refers to a group of disorders in which inflammation damages and can permanently destroy hair follicles, replacing them with scar tissue. Early recognition and treatment are especially important because hair lost after follicular destruction generally cannot regrow.
Congenital Hypotrichosis
Congenital hypotrichosis refers to a group of rare inherited or developmental conditions characterized by reduced, sparse or abnormal hair growth beginning at birth or early in life. These disorders may affect the scalp alone or occur as part of a broader genetic condition.
Hair Shaft Defects
Hair shaft defects are inherited or acquired abnormalities that weaken or alter the structure of the hair fiber and can cause fragility, excessive breakage or the appearance of hair loss. Hair can also be damaged by repeated physical, chemical or cosmetic trauma.
Infectious Agents
Fungal, bacterial and other infectious conditions can affect the scalp, hair shaft or hair follicles and may cause scaling, inflammation, breakage and hair loss. Some infections can result in permanent scarring when severe or left untreated, making accurate diagnosis and appropriate treatment important.
Why Accurate Diagnosis Matters
Different forms of hair loss can produce remarkably similar patterns of thinning or shedding while requiring very different approaches to treatment. Androgenetic alopecia, telogen effluvium, alopecia areata, scarring alopecia, infection, traction and systemic disease can sometimes overlap, and more than one condition may be present at the same time.
Effective treatment begins with identifying what is actually happening to the hair follicle and why. Depending on the presentation, evaluation may include examination of the scalp and hair, trichoscopy, medical history, laboratory testing or scalp biopsy.
The goal is not simply to identify that hair is being lost, but to determine the underlying process before valuable time, money or remaining hair is lost pursuing the wrong treatment.
Hair Science
Hair is biologically far more complex than it appears. Understanding the structure of the hair follicle, the hair shaft and the normal cycle of growth, regression, rest and shedding provides the foundation for understanding why different forms of hair loss occur and how they affect the follicle over time.
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