What causes hair to lose its color?

Why Hair Loses Its Color

Hair loses its color primarily due to age-related depletion of melanocyte stem cells and functioning melanocytes in the hair follicle, resulting in reduced melanin production and transfer to hair shafts. 1, 2

Mechanisms of Hair Color Loss

Primary Causes

• Melanocyte Depletion: Gray and white hair results from a progressive and specific reduction in melanocytes in both the hair bulb and outer root sheath 2
• Oxidative Stress: Age-related imbalance in the hair follicle's ability to handle oxidative stress impacts melanogenesis and melanocyte survival 1
• Melanosome Changes: With aging, melanosomes (structures carrying melanin) undergo morphological changes, becoming larger and rounder 3

Progression of Hair Graying

1. Initial Stage: Decrease in both bulb melanin content and bulb melanocyte population 2
2. Gray Hair Stage: Few melanocytes remain in the bulbs but still express melanin-producing enzymes (tyrosinase and tyrosinase-related protein-1) 2
3. White Hair Stage: Complete absence of detectable melanocytes in the hair bulb 2

Associated Factors and Conditions

Physiological Factors

• Genetic Predisposition: Family history plays a significant role in determining the onset and progression of hair graying 4
• Age: Natural aging process leads to progressive loss of melanocyte stem cells 1

Pathological Associations

• Autoimmune Conditions:

  • Autoimmune thyroiditis can cause hair loss and color changes even with normal TSH levels 5
  • Alopecia areata may selectively target pigmented hairs, sparing gray/white hairs 6

• Nutritional Factors:

  • Nutritional deficiencies can cause the "flag sign" (alternating bands of pigmented and unpigmented hair) 6
  • Iron and vitamin D deficiencies may contribute to hair loss and potentially affect pigmentation 5

• Medical Conditions:

  • Thyroid disorders, even in euthyroid phase, can affect hair pigmentation 5
  • Progeroid syndromes and vitiligo are associated with premature graying 4

External Factors

• Medications: Most drug-induced changes result in lighter hair color, though some medications like PABA and certain chemotherapy regimens can darken hair 6
• Environmental Toxins: Copper exposure can cause green hair discoloration, especially with damaged hair cuticle 6

Diagnostic Approach for Hair Color Changes

• Trichoscopy: Non-invasive examination to assess hair miniaturization patterns and structural changes 5
• Dermoscopy: Can reveal specific features like yellow dots, black dots, and hair shaft diameter variations 5
• Laboratory Testing: Complete blood count, ferritin levels, thyroid function tests, and vitamin D levels when hair loss accompanies color changes 5

Clinical Implications

• Hair graying serves as an early indicator of aging processes that may later manifest elsewhere in the body 1
• The hair follicle pigmentary unit may retain regenerative potential even after producing white hair fibers 1
• Psychological impact of hair color loss should be acknowledged, with appropriate support offered 5

Hair color loss represents a complex interplay of genetic, metabolic, and environmental factors affecting the melanocyte population and function in hair follicles. While primarily associated with aging, premature graying may signal underlying health conditions that warrant investigation.