Estrogen decline is the primary driver. Estrogen maintains vaginal wall thickness, elasticity, and the mucous membrane that produces natural lubrication. When estrogen drops — during menopause, breastfeeding, after oophorectomy, or from certain medications — the tissue atrophies. The walls thin from multiple cell layers to just a few, moisture production slows dramatically, and pH shifts create vulnerability to irritation and infection.

Vascular changes compound the problem. Healthy vaginal tissue depends on robust blood flow for moisture, nutrient delivery, and cellular turnover. As blood flow diminishes, the tissue's self-renewal capacity drops — creating a cycle where thinning tissue receives less blood, which causes further thinning.

Collagen loss in vaginal tissue follows the same pattern as facial skin — approximately 1% per year after 25, accelerating after menopause. The collagen matrix that provides structure, elasticity, and moisture retention breaks down, and the body's ability to replace it diminishes.