Why do fleas bite some people only? - briefly
Fleas preferentially target individuals who emit higher levels of heat, carbon dioxide, and specific skin chemicals such as certain fatty acids and bacterial by‑products. These cues vary among people, making some more attractive to the insects than others.
Why do fleas bite some people only? - in detail
Fleas select hosts based on a combination of chemical, physiological, and environmental cues. Their mouthparts are adapted to pierce the skin of mammals, but they do not feed indiscriminately.
First, skin secretions play a crucial role. Human sweat contains a mixture of lactic acid, ammonia, urea, and fatty acids. The concentration of these compounds varies between individuals due to genetics, diet, and hygiene habits. Fleas are attracted to higher levels of lactic acid and certain fatty acids, which act as olfactory signals that guide them toward the host.
Second, body temperature influences host preference. Fleas detect infrared radiation and are drawn to warmer areas of the body. People with higher peripheral skin temperature, often caused by increased blood flow or metabolic rate, present a more attractive target.
Third, carbon‑dioxide output serves as a long‑range attractant. Individuals who breathe more heavily—such as during exercise or due to respiratory conditions—release greater amounts of CO₂, enhancing their visibility to fleas.
Fourth, skin microbiota affect susceptibility. The bacterial composition on the skin metabolizes sweat components, producing volatile organic compounds (VOCs). Specific bacterial profiles generate VOCs that are especially enticing to fleas, while others emit repellent odors.
Fifth, immune response can modify bite likelihood. Some people develop a rapid inflammatory reaction that releases histamine and other mediators, creating a localized environment that may deter further feeding. Others exhibit a muted response, allowing fleas to feed longer before being detected.
Lastly, environmental exposure matters. Individuals who spend more time in flea‑infested habitats—such as homes with pets, barns, or outdoor areas with wildlife—have higher contact rates. Repeated exposure can sensitize fleas to the particular host’s cues, reinforcing selective biting.
In summary, host selection by fleas results from:
- Chemical attractants in sweat and skin secretions
- Elevated body temperature and localized heat
- Increased carbon‑dioxide emission
- Specific skin‑microbe‑derived volatile compounds
- Variable immune and inflammatory responses
- Frequency and duration of exposure to flea‑rich environments
These factors interact, producing the observed pattern where only certain people receive bites while others remain largely untouched.