Why do mosquitoes bite some people more than others? And why do horseflies, blackflies, midges, and ticks go after certain people every time? They’re reading your body chemistry like an open lab report. Mosquitoes lock onto CO₂ from your breath, heat from your skin, and volatile organic compounds (VOCs) 🧪 you release, many made by your own microbes. Gut imbalances like SIBO or Candida can pump out acetone, acetaldehyde, hydrogen sulfide, and trimethylamine (TMA). These leak into blood, exit in sweat and breath, and create scent profiles insects evolved to find. TMA gives a fishy odor, while hydrogen sulfide smells like rotten eggs 🥚 both are potent cues for biting flies and midges. Fungi and yeasts can produce 1-octen-3-ol, “mushroom alcohol” 🍄, a major mosquito attractant. Hormonal changes (ovulation, pregnancy, or HRT) can increase skin perfusion and raise local skin temperature by 0.3–0.7°C 🔥 This heat accelerates evaporation of lactic acid and carboxylic acids, intensifying the odor plume bugs follow. Sweat chemistry is a microbial buffet 🍽️ Lactic acid, urea, and fatty acids (like isovaleric acid) are eaten by Staphylococcus and Corynebacterium, which turn them into carboxylic acids key attractants for Aedes aegypti. Your skin microbiome 🧴 is shaped by daily habits. Harsh detergents, antibacterial soaps, and overwashing strip diversity, letting dominant odor-producers take over. Wearing unwashed synthetic gym clothes lets Corynebacteria ferment sweat into stronger fatty acids. Other cues: horseflies and deerflies cue in visually on dark, moving shapes 🐴 but also detect octenol and phenolic compounds; ticks sense CO₂ and ammonia with their Haller’s organs; blackflies and midges are drawn to high lactic acid and skin warmth near the head and neck. Your chemical “fingerprint” is always changing 🎭, shaped by microbes, hormones, immunity, hygiene, fabrics, and even your laundry products. Bugs can read it faster than you can swat them. If we ever end up at a cottage together 🏕️ I’ll be counting how many insects orbit your head…and I’ll know exactly why. It’s not always a good thing or a bad thing. It’s just biology and chemistry.