My Husband Has Lost 1/3rd of His Eyebrows — Why?

My husbands eyebrows have balded about a 1/3 from the outside. What would make this happen?

Loss of eyebrow hair, especially the outer edge, may be caused from plucking it, or possibly evenhypothyroidism (low levels of thyroid hormones). Hypothyroidism is treatable by hormonal replacement. Eyebrow loss could also happen as a result of other diseases and conditions such as medications, endocrine diseases, autoimmune disorders, infections, inflammatory conditions and vitamin and mineral deficiencies.