It comes from the bacteria in your skin. These bacteria eats the skin cells in your underarms and releases a chemical called 3-methyl 2-hexenoic acidÃÂ¢Ã¢âÂ¬ which triggers the odor. Bacteria mixed with sweat, joined by the air equals a pungent and awful smell. The only solution is maintaining a proper hygiene. Poor hygiene can cause smelly underarms.