Introduction

Alopecia is defined as a hair loss in an area where hair is expected to grow. The most commonly known symptom is hair loss on the scalp, but alopecia can also cause hair loss in other areas. This article will aim to give an overview of different types of alopecia. 

Alopecia can be broadly categorised as either scarring or non-scarring. Scarring alopecia involves the permanent destruction of the hair follicle, resulting in permanent hair loss. Non-scarring is when the hair follicle is not destroyed, so hair regrowth can be possible. Non-scarring is the more common presentation.

Types of non-scarring alopecia 

Androgenetic alopecia

Androgenetic, or androgenic alopecia, is the term for age-related hair loss, which is dictated by sex hormones. In those assigned male at birth, the hair is generally lost from the temporal areas on either side of the forehead and the top of the crown. In patients assigned female at birth, hair generally thins around the central part of the scalp and the crown. This is the most common type of alopecia in both sexes. It affects around 50% of people assigned male at birth over the age of 50. In people assigned female at birth, around 75% of those over the age of 65 (largely influenced by menopause)

Traction alopecia

This is caused by tension that pulls on the hair. Certain hairstyles where the hair is pulled tight and is under tension over long periods of time can cause this. For example, tight ponytails can end up causing a receding hairline or braids that keep the hair in one position. Hair extensions that are woven or clipped onto the hair can also cause traction alopecia. 

Telogen effluvium 

This is a type of alopecia which causes a global loss of hair (from all over the head rather than just one area. This can be caused by stress (such as a stressful life event serious illness, or can happen during pregnancy) or lack of adequate nutrition (which itself can cause stress to the body’s physiology). The normal hair follicle goes through different phases during its life cycle. The first phase is of growth from the follicle (the root in the scalp), the second phase is when the hair loses its blood supply, and the third phase (known as telogen) involves the shedding of the hair. Telogen effluvium is where the hair follicles are stuck in the telogen stage of their growth and continue to shed. The onset of this type of alopecia can happen at the time of the stressful event or can start up to 3 months after. The regrowth can happen after the stress is over, and the body can return to normal physiology.

Alopecia areata 

Alopecia areata is an autoimmune disease in which the body’s immune system attacks the hair follicles, causing hair to shed in a patchy manner, leaving bald areas. The timings of the “attacks” can be at random. The hair loss, however is not always permanent - it is a relapsing-remitting disease- once the immune response calms down, hair can regrow. 

Scarring alopecia

Scarring alopecia causes permanent hair loss. This can be all over the body, not just on the scalp. Scarring alopecia is also known as cicatricial alopecia. There are two categories of cicatricial alopecia- primary cicatricial alopecia refers to when the body attacks its own hair follicles. There is also secondary cicatricial alopecia, where some external factor destroys the hair follicle. In both types, the hair follicle is replaced by scar tissue and so cannot regenerate.

Primary cicatricial alopecia (PCA) 

PCA is caused by immune cells which attack the hair, and is categorised by which type of cell is involved- lymphocytes, neutrophils or mixed (a combination of both). The exact reasons as to why this happens are not fully understood. The diagnosis of which type of PCA is determined via a biopsy of the skin on the scalp (a small section of the skin is taken for analysis in a lab). 

The most common type of PCA is Lichen planopilaris. This is a type of lymphocytic alopecia. Symptoms include redness and keratosis ( a thickening of the skin, like scaling ) of the scalp. The areas may also be itchy and painful. This can cause global or patchy hair loss, and the scalp becomes smooth and shiny due to the scarring. One subtype of Lichen planopilaris is known as frontal fibrosing alopecia (FFA). It mostly affects people assigned female at birth after menopause and causes a receding hairline.

There is another type of PCA which can occur as part of Lupus- a systemic autoimmune condition. This also causes redness and keratosis of the scalp.

Neutrophilic scarring alopecia involves pus forming around the hair follicles- the pus that is in acne spots is mostly made of neutrophils. This is like a similar immune response around the hair. Like in acne, after the infection is cleared, scars form, and in this case, hair follicles are destroyed. A similar response is seen with mixed aetiology PCA.

Medications such as steroids, anti-inflammatory drugs or immunosuppressants can be used in these cases to control the disease process and minimise hair loss, but any damage that is already done will not be reversible.

Secondary cicatricial alopecia

Secondary cicatricial alopecia is irreversible hair loss due to some external factor or trauma. This can be due to an accident or injury burns (thermal or chemical). Chemotherapy and radiotherapy, which are often used for cancer, can cause hair loss- in some people, it can be permanent (but not always), or hair can grow back in patches. Certain infections (note: infections due to a known pathogen, rather than the body attacking itself, thinking there is an infection), such as cellulitis or tinea capitis, can cause permanent hair loss. Other conditions, such as psoriasis or scleroderma, that affect the skin can cause alopecia too. As with PCA, medications can be taken to control the disease processes and any systemic infections to minimise hair loss.

Psychological impact and a note on trichotillomania

Psychologically, alopecia can significantly affect quality of life. Evidence shows that people experiencing alopecia can also have concurrent anxiety, depression and/or social isolation. Hair (especially) on the scalp is very much a part of “normal” appearance and daily life, and not having this can have very negative consequences. Wigs and potentially hair transplants are sometimes an option but may not be in all cases.

Trichotillomania is an obsessive-compulsive disorder which involves the urge or obsession with pulling out one’s own hair. This can present like alopecia but can have any pattern of hair loss around the scalp or in different areas of the body. The type of hair loss is a non-scarring alopecia. However, unlike the aforementioned types of alopecia, trichotillomania is a psychiatric condition.

Summary

Alopecia is a term referring to conditions that result in the loss of hair where hair would be expected to be. There are many different types of alopecia. Alopecia can be broadly classified as non-scarring, where the hair loss is not permanent, and the follicle is not destroyed, or scarring, where hair loss is permanent and the follicle is destroyed and later replaced by scar tissue.

The most common type of alopecia overall is androgenic alopecia, which is otherwise known as age-related hair loss, e.g. male-pattern balding or female-pattern balding. This is a non-scarring alopecia. Other types of non-scarring alopecia include alopecia aerata- an autoimmune condition that results in periodic patchy shedding of hair, which can later regrow. Telogen effluvium is another type where the hair sheds evenly all over the head (as opposed to in patches) in response to a stressful event or period of life. The last type is traction alopecia, which occurs as a result of certain hairstyles or extensions pulling the hair over long periods of time, eventually causing the hair to fall out in those areas.

The most common type of scarring alopecia is lichen planopilaris, which is an autoimmune reaction where the body destroys the hair follicles, and the scalp becomes smooth and shiny. Other types involve a similar infection-like response where the scalp becomes red, itchy, flaky, painful and sometimes with areas of pus as the hair falls out.