Taipei in May and in June both sit at 82% relative humidity — identical. But absolute humidity is 18.6 and 21.5, nearly 3 g/m³ apart.

The same '82%' puts your skin in two different kinds of air. This is exactly why relative humidity can't be the basis of a routine: it's a ratio, not an amount.

What the rainy season actually does

High humidity doesn't hydrate you. What it does is stop sweat evaporating. Sweat stays on the surface, mixed with sebum and with whatever you applied that morning, forming a film that neither dries nor leaves.

Something else runs alongside it: under sustained high humidity, corneocytes take on water and swell, and the lipid barrier softens. The barrier structure loosens and irritates more easily. So sensitivity in the rainy season and sensitivity in a dry season have opposite causes — one is waterlogged, one is parched.

So almost everything that goes wrong in this season is downstream of being closed in — congestion, breakouts, flushing, makeup sliding, plus that waterlogged sensitivity. None of it is dehydration, yet it gets treated as dehydration, and gets worse.

The mirror-image mistake: because the air feels wet, people drop hydration entirely for the month. Water in the air doesn't reach the stratum corneum. Drop it and you end up oily on top and dry underneath.

The four levers

1. QuantityLess of each, not fewer steps. Keep the structure; make every layer thinner. The aim is to give it a chance to dry.
2. TimingKeep daytime light and handle richness at night. A daytime face in this season needs to breathe, not be covered.
3. OrderCleanse thoroughly, but not more often. What being closed in produces can't be solved by adding — or by washing more. Over-wash and the barrier takes more damage than the rain ever did.
4. IntervalAfter rain or sweat, don't go straight to touching up. Deal with the tacky layer first.

When humidity is high, what skin lacks usually isn't water — it's somewhere for the water to go.
Get the direction wrong and everything you do thickens the film.