Sweat breaks down makeup because perspiration contains salts and oils that dissolve traditional cosmetic formulas, causing foundation, eyeliner, and blush to slide, fade, or streak within hours. Humidity and heat accelerate this process, making everyday makeup unreliable during active lifestyles, outdoor events, or warm climates. Switching to the best waterproof makeup products formulated with sweat-resistant ingredients creates a durable barrier that stays intact through moisture and movement.