Acne is more severe in hot, humid climates. Heat and humidity have such an aggravating effect on acne because the bacteria thrive in hot, moist environments. They use your oil like they are sipping on a piña colada. What is known is that the stratum corneum (the tough outer layer of our skin) swells tremendously under humid conditions. In fact, the stratum corneum can swell up to 300% when immersed in water.You know what happens when you swim for several hours or soak a long time in the tub. The soles of your feet and your palms (where the stratum corneum is especially thick) become puffy and ridged from expansion. Though it is less perceptible, the same swelling occurs throughout the rest of your skin. What may happen is that the pressure from the swelling can lead to a breakdown in a vulnerable follicle wall.