Hair loss associated with thyroid disorders
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Thyroid Disorders and Hair Loss: Key Associations
Thyroid disorders, including both hypothyroidism and hyperthyroidism, are strongly linked to various forms of hair loss. The most common types of hair loss associated with thyroid dysfunction are telogen effluvium, alopecia areata, and androgenetic alopecia. Thyroid hormones play a crucial role in the growth, differentiation, and metabolism of hair follicles, making the skin and hair particularly sensitive to changes in thyroid function. Both underactive and overactive thyroid states can lead to widespread hair shedding, and the prevalence and impact of this association are often underestimated in clinical practice 159.
Mechanisms: How Thyroid Dysfunction Affects Hair Growth
Thyroid hormones directly influence the hair growth cycle. In hypothyroidism, there is an increase in the percentage of telogen (resting phase) hairs, which leads to diffuse hair shedding. This imbalance is reversible with thyroid hormone replacement therapy, which restores normal hair growth patterns. The effect is mediated by the hormone’s impact on both the initiation and duration of hair growth cycles 25. At the cellular level, hypothyroidism reduces cell proliferation in hair bulbs, while hyperthyroidism increases it, further demonstrating the direct effect of thyroid status on hair growth .
Types of Hair Loss Linked to Thyroid Disorders
Several types of hair loss are associated with thyroid dysfunction:
- Telogen Effluvium: Often seen in both hypothyroidism and hyperthyroidism, characterized by diffuse hair shedding 19.
- Alopecia Areata: Shares an autoimmune background with autoimmune thyroid diseases, and may be more severe in the presence of thyroid anomalies .
- Androgenetic Alopecia and Frontal Fibrosing Alopecia: These may also have higher prevalence in individuals with thyroid disorders, especially in women and postmenopausal cases .
Clinical and Dermoscopic Findings in Thyroid-Related Hair Loss
Patients with hypothyroidism commonly present with diffuse hair loss, coarse hair, and other skin changes. In hyperthyroidism, hair tends to be thin and soft. Dermoscopic studies show that hypothyroid patients with hair loss have more hair shaft abnormalities, increased vellus hair, and signs of inflammation compared to those with normal thyroid function 48. These findings suggest that dermoscopy can help detect subtle changes in hair and scalp health related to thyroid dysfunction .
Prevalence and Screening Recommendations
Studies indicate that a significant number of patients with diffuse hair loss have underlying thyroid dysfunction, especially when other systemic diseases are present. Screening for thyroid disorders is recommended in adult women presenting with unexplained diffuse hair loss, as abnormal thyroid function is found in a notable proportion of these cases 38. However, routine thyroid screening in asymptomatic patients with alopecia areata remains controversial unless there is a personal or family history of autoimmunity .
Molecular Insights: The Hairless Gene and Thyroid Hormone Receptors
The hairless (hr) gene, which is critical for hair maintenance, acts as a corepressor for thyroid hormone receptors. Mutations in this gene can lead to specific hair loss syndromes, highlighting the molecular connection between thyroid hormone signaling and hair follicle health .
Direct Effects of Thyroid-Stimulating Hormone (TSH) on Hair Follicles
Human hair follicles express receptors for TSH, indicating that TSH can directly influence hair follicle function beyond its classical role in thyroid hormone regulation. This suggests a more complex, nonclassical pathway by which thyroid dysfunction can impact hair growth .
Conclusion
Thyroid disorders are a significant and often underrecognized cause of hair loss. Both hypothyroidism and hyperthyroidism can disrupt the normal hair growth cycle, leading to various forms of alopecia. Clinical, dermoscopic, and molecular evidence all support the close relationship between thyroid function and hair health. Early recognition and management of thyroid dysfunction are essential for improving hair loss outcomes and overall patient well-being. Further research is needed to better understand the mechanisms and to refine diagnostic and treatment strategies for hair loss associated with thyroid disorders 149.
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