In your 40s, skin becomes dull-looking, uneven, and yes, fine lines and wrinkles are more predominant as you move into and through your forties. This change is primarily due to perimenopause (the years leading up to menopause), a period when your estrogen levels begin to decrease, and skin becomes thinner and begins to lose its elasticity.
Wrinkling can also be associated with how well you took care of your skin in your 20s and 30s, including whether or not you protect your skin from the sun’s harmful rays.