I get this one all the time — usually from women in their late thirties or forties who have never had dry skin before, and suddenly the moisturizer that used to work stopped working overnight.
When sudden dryness shows up in an adult woman, it's almost always one of three biological drivers.
1. Estrogen is dropping. Estradiol supports the natural moisture-retaining function of the epidermis. When it starts fluctuating in perimenopause or drops sharply at menopause, women often notice dryness before anything else. This pattern is often paired with earlier wake-ups, a slightly slower metabolism, and cycle changes.
2. Omega-3 status is low. The EPA and DHA in your red blood cell membranes are also the fatty acids that support your skin's barrier function. When omega-3 is low, transepidermal water loss rises — meaning your skin literally loses more water to the air than it should (Pilkington, 2011). Dryness that moisturizer doesn't fix.
3. The barrier got disrupted. Over-cleansing, over-exfoliating, harsh actives, a new retinoid, seasonal humidity drop, hot showers. Any of these can strip the lipid layer that holds moisture in.
What to do about it: measure your estradiol and omega-3 index, and look honestly at your routine for barrier disruption. The blood work usually tells you exactly what's happening. Both estradiol and the omega-3 index are on the JenSkin panel.