Introduction

Hypotrichosis is a condition characterised by a scarcity of hair in which hair typically grows normally. Still, hair loss occurs with age in areas such as the scalp, eyelashes, and eyebrows. It is a developmental disorder that begins in early childhood and progresses to hair loss by adulthood. Hypotrichosis is an autosomal dominant condition not associated with other developmental hair loss syndromes.¹ Another term used for hair loss is alopecia, which refers to absolute hair loss after normal growth, whereas hypotrichosis is the presence of less hair than normal.²

Types of Hypotrichosis

Hypotrichosis is categorised as syndromic,  non-syndromic and other types. 

• Syndromic hypotrichosis is a type of hypotrichosis present along with other physical abnormalities, metabolic, or mental disorders. This includes Marie Unna hypotrichosis (MUH),  a form that appears to be hereditary and is often observed from childhood onwards and  Ectodermal Dysplasias (EDs), a broad category of inherited conditions that affect the development of ectodermal structures and related appendages, including hair⁴
• Non-Syndromic Hypotrichosis is characterised by sparse hair as the primary or sole symptom, without associated systemic problems. Examples include hypotrichosis simplex, a rare hereditary disorder characterised by progressive thinning of the hair shaft. Hypotrichosis with juvenile macular dystrophy (HJMD) is a genetic disorder that causes both hypotrichosis and early-onset visual impairment⁴
• Hypotrichosis with Hair Shaft Structural Abnormalities. This is a group of genetic conditions where there is an inherent defect in the hair structure, leading to fragility and hair loss. Some examples are Woolly Hair, characterised by abnormally kinky, sparse, and wiry hair. Loose Anagen Syndrome (LAS) features hair that is easily pulled from the follicle due to dysplastic hairs. Trichorrhexis nodosa, a condition with abnormal hair shaft fracturing⁴

Causes

Hypotrichosis is caused by a genetic mutation in the DNA. It can be inherited in different patterns, including autosomal dominant (requiring only one faulty copy of a gene) or autosomal recessive (requiring two faulty copies). Hypertrichosis can be caused by a mutation in the  LSS, APCDD1, LIPH, LPAR6, or DSG4 gene.³ These genes instruct the protein formation involved in the growth, division, and maturation of cells within hair follicles. Mutations in these genes result in abnormal protein production, which can not help in the development of hair follicles. 

Several environmental factors can also be responsible for hair loss. Factors like chemicals, pollution, minerals, weather, and sun exposure can cause thinning of hair and eventually loss of hair.

Clinical Approach

The initial step in diagnosing hypotrichosis is to examine whether the hair loss is a symptom or a syndrome. A patient's history and physical examination can be useful in narrowing it down. A time course can be established by inquiring about the onset of hair scarcity, its duration, rate of progression, and whether there was a period of normal hair.⁴

Additional investigation to clinical examination

Hair pull test

The regular hair pull test involves gentle traction by passing the examiner's finger through the hair to assess the degree of active shredding. It is a crude technique. A positive test typically indicates telogen hair shedding and remains a valuable component of the clinical examination.  A forced hair-pull test provides a more standardised assessment. The examiner pulls around 50-60 hairs slowly and firmly from root to tip. The test is positive if more than 10% of hair or more than three hairs from multiple scalp sites are easily extracted, indicating active hair loss. 

The removed hairs are examined under contrasting backgrounds (white for dark hair, black for light hair) to assess tip appearance (blunt or regrown tip), microscopic features to evaluate the proximal hair growth and hair shaft properties for examination of hair thickness, texture, fragility, shape and twists. 

When performed correctly, the hair pull test is a simple and informative method that, alongside clinical history, assists in evaluating the type and severity of hair loss.⁴ 

Loose Anagen Hair Pull Test

It is a specific diagnostic test to examine poorly anchored hair and to confirm loose anagen syndrome. In this test, about 10–20 hairs are firmly grasped close to the scalp, and an attempt is made to extract them with steady traction. In individuals with normal hair, anchoring the hairs resists removal. In contrast, patients with loose anagen syndrome show easy extraction of hairs with little or no discomfort. This is a simple test that provides a rapid and reliable clue to diagnosing loose anagen syndrome.⁴

Trichogram

This traditional procedure involves grasping 25–50 hairs close to the scalp and extracting them swiftly in the direction of growth. The hair bulbs were then mounted on a glass slide and examined under light microscopy to determine the anagen-to-telogen ratio. A telogen count above 35% (normal range: 10–20%) was considered indicative of telogen effluvium. 

Trichogram is a painful procedure and has several limitations, and now it has been replaced by a trichoscopy examination.⁴

Trichoscopy 

It is a non-invasive dermoscopic technique used to examine the hair and scalp for structural abnormalities. By applying a handheld dermatoscope to the scalp, clinicians can visualise hair shafts, follicular units, perifollicular skin, and cutaneous microvasculature under magnification. Trichoscopy is now recommended as the primary diagnostic tool for hair disorders and is often supplemented with hair-pull tests.⁴  

Scalp Biopsy

This test is performed using a 4 mm patch from the affected area, followed by histological staining. This allows examination of the entire hair follicular unit down to the subcutaneous fat, providing valuable information when differentiating between acquired scarring and non-scarring alopecias, as well as conditions such as androgenetic alopecia and telogen effluvium.⁴

Genetic Testing 

Genetic testing is rapidly evolving and plays an important role in the diagnosis of hair shaft and hair growth disorders. Next-generation sequencing (NGS) has enabled the identification of numerous inherited hair disorders with well-defined molecular bases. These advances not only improve diagnostic accuracy but also enhance our understanding of disease mechanisms and help identify novel therapeutic targets in the future.⁴

Treatment and Management

There is no specific treatment available for hypotrichosis.⁵ Management may also include hair care techniques, counselling, and genetic counselling.  

Cosmetic options like wigs, hairpieces, and makeup can be used. A hair transplant can be done in case of permanent hair loss. Under a hair transplant procedure, a dermatologist or cosmetic surgeon removes hair from a part of the head that has hair and transplants it to a bald spot.⁴ 

Bimatoprost ophthalmic solution 0.03% is a novel method of increasing the prominence of eyelashes. The effects of treatment are not immediate but can often be observed several weeks after starting therapy. Also, results are not permanent.⁶ Botanical extracts in combination with minoxidil can help in the treatment of hypotrichosis of the scalp.⁷

Recent Advances in Research

Research into hair disorders has expanded rapidly in recent years, and hypotrichosis is an important focus: 

1. Gene study: Identification of genes responsible for hypotrichosis can help in gene therapy⁸  
2. Stem Cell Research and hair follicle engineering: Scientists are investigating to regenerate hair follicles in vitro and transplant them back into patients⁸
3. Molecular pathways: Elucidating the molecular pathways that regulate hair follicle development and function, to identify novel therapeutic targets for hair growth disorders⁸
4. Pharmacological Innovation: Drugs that modulate the hair follicle cycle are under study⁸

Conclusion

Hypotrichosis, though uncommon, has a profound impact on individuals and families. It encompasses a diverse group of conditions, from congenital genetic syndromes to acquired forms caused by autoimmune or environmental factors. While there is no definitive cure, supportive care, cosmetic interventions, and psychological support remain central to management. Advances in genetic research, stem cell technology, and molecular biology hold promise for future therapies. Until then, raising awareness, providing accurate diagnosis, and supporting affected individuals emotionally and socially are crucial steps in improving quality of life.