What are the causes of hair loss in children?

Causes of Hair Loss in Children

Primary Causes

Alopecia areata is the most common autoimmune cause of patchy hair loss in children, accounting for approximately 26% of cases, and is mediated by T lymphocytes attacking hair follicles. 1 The condition presents as round, non-inflamed bald patches with pathognomonic "exclamation-mark" hairs (short broken hairs at the periphery). 2, 1 About 20% of affected children have a family history, and the condition associates with other autoimmune diseases including thyroid disease, lupus, and vitiligo. 3 Importantly, 34-50% of children with limited alopecia areata experience spontaneous regrowth within one year without treatment. 2, 1, 4

Tinea capitis (scalp ringworm) is the most common infectious cause, presenting with patchy hair loss accompanied by scalp inflammation and scaling. 3 This fungal infection requires oral antifungal therapy and mandates fungal culture before treatment initiation, as clinical diagnosis alone is frequently inaccurate and represents the leading cause of therapeutic failure. 3, 4

Trichotillomania (compulsive hair pulling) produces an incomplete, irregular loss pattern with broken hairs that remain firmly anchored in the anagen phase, distinguishing it from alopecia areata where hairs pull out easily. 1, 3, 4

Nutritional and Metabolic Causes

Vitamin D deficiency shows strong association with hair loss, with 70% of alopecia areata patients having levels <20 ng/mL versus 25% of controls. 3 Lower vitamin D levels correlate inversely with disease severity, and the vitamin D receptor plays a critical role in hair follicle cycling. 3

Iron deficiency is the most common nutritional deficiency worldwide causing chronic diffuse telogen hair loss, with serum ferritin levels consistently lower in children with alopecia. 3

Zinc deficiency impairs hair follicle function, with serum zinc levels tending to be lower in alopecia areata patients, particularly those with resistant disease >6 months duration. 3

Thyroid dysfunction (both hypothyroidism and hyperthyroidism) commonly causes hair loss in children. 1 TSH and free T4 should be checked to exclude this reversible cause. 4

Stress-Related and Medication-Induced Causes

Telogen effluvium is stress-induced shedding where physiologic or emotional stressors push hair follicles prematurely into the resting phase. 3 Triggers include illness, surgery, severe emotional stress, rapid weight loss, and nutritional deficiencies. 3 Up to 80% of cases with short duration (<1 year) resolve spontaneously once the trigger is removed. 1

Anagen effluvium occurs when medications (particularly chemotherapy) interrupt actively growing hair follicles, causing rapid and severe hair loss. 3

Mechanical and Traction Causes

Traction alopecia results from tight hairstyles (braids, ponytails, hair extensions) causing chronic pulling on hair follicles. 5, 6 This is particularly common in certain cultural hair-care practices. 7

Congenital and Genetic Causes

Congenital alopecia conditions and ectodermal dysplasias present with hair abnormalities from birth or early infancy. 6, 8 Red-flag features requiring genetic evaluation include: 4

• Premature greying with nail/skin changes, hearing impairment, or signs of early aging (warrants TERT/TERC mutation testing due to elevated systemic cancer risk)
• Short stature, dysmorphic facial features, or thumb hypoplasia (raises suspicion for Fanconi anemia or dyskeratosis congenita)

Systemic Disease-Related Causes

Systemic lupus erythematosus can cause both scarring and non-scarring alopecia. 3 Serology for lupus should be obtained if systemic features such as joint pain, photosensitivity, or facial rash are present. 3

Secondary syphilis presents with patchy "moth-eaten" hair loss, though this is rare in children. 3

Diagnostic Approach Algorithm

Step 1: Pattern Recognition

• Patchy, round bald spots with exclamation-mark hairs → alopecia areata 2, 1
• Patchy loss with scalp inflammation/scaling → tinea capitis 3
• Irregular incomplete loss with firmly anchored broken hairs → trichotillomania 1, 4
• Diffuse thinning over entire scalp → telogen effluvium or nutritional deficiency 1
• Marginal/temporal thinning → traction alopecia 5

Step 2: Dermoscopy Findings

• Yellow dots + exclamation-mark hairs → alopecia areata 1, 3
• Nail pitting, ridging, or dystrophy (present in ~10% of alopecia areata cases) supports the diagnosis 1, 3, 4

Step 3: Targeted Laboratory Testing (only when diagnosis is uncertain or atypical presentation) 2, 1

• Fungal culture if scalp inflammation/scaling present 3, 4
• TSH and free T4 to exclude thyroid dysfunction 1, 4
• Serum ferritin, vitamin D, and zinc levels for nutritional deficiencies 3, 4
• Complete blood count with hemoglobin for hematologic abnormalities 4
• Lupus serology if systemic features present 3

Critical Pitfalls to Avoid

Do not start antifungal treatment without confirmed positive fungal culture, as misdiagnosis is the leading cause of therapeutic failure. 3, 4

Do not order extensive autoimmune panels in straightforward alopecia areata cases, as the modest increase in autoimmune disease prevalence does not justify routine screening. 2, 1

Do not overlook the psychological impact of hair loss on children and families, as it can affect developmental outcomes, self-esteem, and school performance, warranting referral to pediatric psychology when behavioral changes occur. 2, 1, 4

Do not confuse trichotillomania with alopecia areata: trichotillomania shows broken hairs firmly anchored in anagen, whereas alopecia areata displays exclamation-mark hairs that pull out easily. 1, 3