Why do fleas bite one person but not another? - briefly
Fleas are drawn to cues such as carbon‑dioxide output, body heat and particular skin‑derived chemicals; individuals who emit stronger or more attractive versions of these signals receive more bites. Differences in blood type, skin microbiota and personal hygiene modify the profile of these cues, resulting in uneven susceptibility.
Why do fleas bite one person but not another? - in detail
Fleas locate hosts by sensing carbon dioxide, body heat, movement and specific skin chemicals. Individuals who exhale more carbon dioxide or maintain higher skin temperature create a stronger signal, increasing the likelihood of a bite. Skin secretions contain volatile compounds such as lactic acid, ammonia and fatty acids; their concentration varies with genetics, diet and hygiene. People whose skin emits larger amounts of these attractants become preferred targets.
Blood type influences flea feeding behavior. Studies indicate that type O blood releases more attractive odorants than type A or B, prompting more frequent probing. Genetic differences also affect the composition of the skin microbiome, which modulates odor profiles. Certain bacterial strains produce metabolites that amplify flea attraction, while others generate repellent substances.
Immune response determines the visible reaction to a bite. Some hosts mount a vigorous histamine release, producing noticeable welts that reveal the encounter. Others exhibit a muted response, allowing bites to go unnoticed despite occurrence. This disparity can create the impression that fleas avoid particular people.
Flea species display varying host preferences. Cat‑fleas (Ctenocephalides felis) favor felines but will opportunistically bite humans when animal hosts are scarce. Dog‑fleas (Ctenocephalides canis) show similar flexibility. Environmental factors—such as indoor heating, humidity levels and the presence of animal bedding—affect flea activity and consequently the exposure risk for different occupants.
Personal habits modify risk. Wearing loose clothing permits easier access to skin, while tightly woven fabrics provide a barrier. Regular grooming removes flea larvae and reduces odor accumulation on hair and skin. Use of repellents containing permethrin or essential oils creates a chemical deterrent that some individuals apply more consistently than others.
In summary, the variation in flea biting among people results from a combination of physiological signals (CO₂ output, heat, skin chemistry), genetic factors (blood type, microbiome), immune sensitivity, flea species behavior, environmental conditions and personal protective measures. Each factor contributes to the probability that a flea will select one individual over another.