Why do fleas bite one person and not another? - briefly
Fleas respond to individual chemical signals—body heat, carbon dioxide output, and skin secretions—so people who emit stronger or more attractive cues are bitten more often. Higher concentrations of certain fatty acids or reduced grooming can also increase a person's appeal to the insects.
Why do fleas bite one person and not another? - in detail
Fleas locate a host by sensing heat, carbon‑dioxide, movement, and chemical cues emitted from the skin. Individuals who generate higher body temperature, exhale more CO₂, or produce greater amounts of skin secretions create a stronger attractant gradient, leading to more frequent contact.
Key physiological and environmental variables influencing bite distribution:
- Blood type – certain blood groups contain surface antigens that fleas detect more readily.
- Skin microbiota – bacterial colonies break down sweat into volatile compounds; a diverse or abundant microbiome can increase the concentration of these attractants.
- Sweat composition – higher concentrations of lactic acid, ammonia, or fatty acids enhance flea orientation.
- Body heat – elevated peripheral temperature raises infrared emission, drawing fleas from a distance.
- Carbon‑dioxide output – larger individuals or those engaged in physical activity exhale more CO₂, a primary flea cue.
- Genetic factors – variations in genes controlling odorant receptors affect how strongly a person is perceived.
- Immune response – some people develop pronounced inflammatory reactions, making bites more noticeable; others experience mild or no reaction, giving the impression of fewer bites.
- Clothing and grooming – tight fabrics or frequent bathing can reduce flea access to skin, while loose clothing may provide easier entry points.
- Proximity to animal hosts – living with pets or in environments with rodents increases exposure; people who avoid these settings encounter fewer fleas.
Fleas are opportunistic parasites. When their preferred hosts (dogs, cats, rodents) are scarce, they will bite humans as a secondary option. Consequently, a person who spends time in infested areas or handles infested animals is more likely to be bitten, regardless of personal attractant levels.
In summary, bite frequency results from a combination of host‑derived signals, individual physiological traits, immune sensitivity, and environmental exposure. Differences in any of these factors can explain why one person receives multiple bites while another remains largely untouched.