What to watch with FT3 and skin aging?

FT3 (free triiodothyronine) is the active thyroid hormone and influences skin metabolism via thyroid hormone receptors in fibroblasts and keratinocytes. Optimal FT3 levels support collagen synthesis, cell turnover, and moisture balance. Both hypothyroidism (dry, scaly skin, increased wrinkling) and hyperthyroidism (thin, fragile skin, increased vascularity) can accelerate skin aging. However, evidence for a direct causal link between FT3 and skin aging is primarily mechanistic and based on observational studies. Clinically relevant effects usually occur only with overt thyroid dysfunction. A single FT3 value without TSH and fT4 is of limited use. For skin aging concerns, focus on lifestyle factors (UV protection, diet, smoking cessation) rather than isolated FT3 optimization. Caution: No evidence supports thyroid hormone supplementation for skin rejuvenation in euthyroid individuals.