On a warm, humid day, why can a 27 °C room feel worse once your skin is sweaty?
Show answer & explanation
Answer: Sweat evaporates less readily
Humid air stores less heat — Humid air can feel heavy and sticky, but the sharp discomfort after sweating is not mainly caused by air storing less heat. Air’s ability to absorb heat affects convection, yet that does not explain why wet skin stops cooling. The dominant problem is that sweat cannot evaporate as easily into already moist air.
Sweat forms an insulating layer — Sweat can make skin feel sticky and make clothes cling, so it is easy to imagine it acts like an insulating layer. Sweat cools only when liquid water turns into vapor and carries latent heat away from the skin. If evaporation is blocked, the sweat stays wet but does not remove much heat.
Sweat evaporates less readily ✓ — When sweat evaporates, it carries heat away as water vapor leaves the skin. High humidity means the air already contains a lot of water vapor, so the vapor-pressure difference between skin and air is smaller. Sweat then evaporates more slowly, cooling weakens, and the 27 °C room feels worse.
More Physics in Daily Life questions
- In a warm office that already reads 26 C, which change can make people feel cooler without lowering the thermostat?
- Why might 26 C feel acceptable in a breezy naturally ventilated summer building but too warm in a sealed winter office?
- Why can moving air make a 27 C room feel cooler without changing the thermometer?
- Why can a desk beside a cold window feel chilly even when the thermostat across the room still reads 22 C?
- In the same 22 C room, why might someone who just climbed stairs feel warm while someone sitting in a T-shirt feels chilly?
- Why does a quiet seated person still count as a heat source in a 22 C office?