Why do bed bugs bite some people and not others?

Understanding Bed Bug Bites

What are Bed Bugs?

Anatomy and Biology

Bed bugs locate hosts using a suite of sensory organs that detect heat, carbon‑dioxide, and volatile organic compounds emitted from the skin. The insect’s antennae contain chemoreceptors tuned to specific chemical signatures, while specialized sensilla on the tarsi respond to temperature gradients. When a potential host’s cues exceed the detection threshold, the bug initiates probing and insertion of its proboscis.

Human skin releases a complex mixture of substances that influence attractiveness to the insect. Key biological factors include:

• Blood type – certain antigens correlate with higher levels of skin‑derived odorants.
• Cutaneous microbiota – bacterial metabolism produces volatile acids and aldehydes that can act as attractants.
• Sweat composition – variations in lactic acid, fatty acids, and ammonia affect the chemical landscape.
• Carbon‑dioxide output – metabolic rate determines exhaled CO₂, a primary long‑range cue.
• Skin temperature – localized heat signals a blood‑rich feeding site.
• Immune response – individuals with heightened histamine release may experience more pronounced bite reactions, making bites more noticeable.

The proboscis of a bed bug consists of a fascicle of thin stylets that penetrate the epidermis and dermis to reach capillaries. Salivary secretions contain anticoagulants, vasodilators, and anesthetic proteins that facilitate blood uptake and reduce host awareness. Variability in host skin thickness and vascular density can affect the ease of feeding, thereby influencing bite incidence.

Differences among people arise from the interaction between these anatomical and biochemical variables. A person whose skin emits fewer attractive volatiles, produces lower CO₂ levels, or possesses a less favorable microbial profile presents a weaker signal to the bug’s sensory system, reducing the likelihood of a bite. Conversely, individuals whose physiological profile matches the insect’s detection thresholds become preferred targets.

Life Cycle and Habits

Bed bugs (Cimex lectularius) develop through five distinct stages: egg, first‑instar nymph, second‑instar nymph, third‑instar nymph, fourth‑instar nymph, and adult. Each molt requires a blood meal, making feeding essential for progression. The cycle lasts approximately 4–6 weeks under optimal temperature (24–30 °C) and humidity (40–80 %).

• Eggs: Laid in clusters on fabric seams, walls, or crevices; hatch in 6–10 days.
• Nymphs: Six instars, each requiring a fresh bite to molt; growth is rapid when hosts are readily available.
• Adults: Live up to a year without feeding; capable of producing 200–500 eggs over their lifespan.

Bed bugs are nocturnal, seeking hosts when humans are immobile and body heat rises. They locate victims by detecting carbon dioxide, heat, and skin odor. After feeding, they retreat to hidden refuges to digest, molt, or lay eggs. Their preference for tight harborages (mattress seams, baseboards, furniture cracks) reduces exposure to disturbances and facilitates rapid colonization.

Feeding frequency varies among individuals because bed bugs respond to cues that differ among people. Factors such as skin temperature, emitted carbon dioxide levels, and specific skin chemicals influence attraction. Consequently, some hosts receive multiple bites while others may remain untouched, despite the insects’ identical life‑stage requirements.

The Act of Biting

How Bed Bugs Feed

Bed bugs locate a host by sensing body heat, carbon‑dioxide, and movement. Their antennae and maxillary palps contain chemoreceptors that detect these cues, guiding the insect toward exposed skin.

When the bug contacts the skin, it inserts a pair of elongated, needle‑like mouthparts called stylets. The stylets penetrate the epidermis and dermis, creating a narrow channel that bypasses pain receptors. Through this channel the bug delivers a complex saliva that contains anticoagulants, vasodilators, and anesthetic compounds. The saliva prevents clotting, expands blood vessels, and temporarily numbs the bite area, allowing uninterrupted feeding.

The feeding phase proceeds as follows:

1. Probe – stylets are positioned and saliva injected.
2. Engorgement – the bug draws blood into its distended abdomen; a single meal can yield up to five times its body weight.
3. Detachment – after reaching fullness, the bug retracts its mouthparts and retreats to a hiding place.

The duration of a blood meal ranges from five to ten minutes, depending on temperature and host availability. After feeding, the insect digests the blood over several days, converting it into proteins needed for egg production and molting. The efficiency of this process, combined with the composition of the host’s skin secretions and immune response, determines whether a bite produces a noticeable reaction.

Saliva and Anticoagulants

Bed‑bug saliva contains a complex mixture of bioactive molecules that facilitate blood acquisition. The primary components include:

• Anticoagulant enzymes that inhibit the coagulation cascade, preventing clot formation at the feeding site.
• Vasodilators that expand capillaries, increasing blood flow to the puncture.
• Analgesic peptides that suppress the host’s pain receptors, reducing detection.
• Immunomodulatory proteins that dampen local inflammatory responses.

These substances act synergistically to keep the wound open and fluid, allowing the insect to ingest blood uninterrupted. Human sensitivity to these agents varies widely. Individuals with heightened immune reactivity produce stronger histamine release when exposed to the salivary proteins, resulting in visible welts and itching. Conversely, persons with a muted immune response may experience little or no reaction, giving the impression that the bug did not bite them.

Variability in host response also depends on skin characteristics. Thicker epidermis or higher levels of natural skin lipids can impede the penetration of the proboscis, limiting saliva delivery and reducing the likelihood of a noticeable bite. Genetic differences influencing the expression of receptors for the salivary peptides further modulate the intensity of the reaction.

In summary, the effectiveness of bed‑bug saliva in preventing clotting and masking the bite determines feeding success, while individual immune and skin factors dictate whether a bite becomes apparent. The interplay of these mechanisms explains the observed disparity in bite reactions among different people.

Factors Influencing Bed Bug Preferences

Human Skin Chemistry

Pheromones and Odor Profiles

Bed bugs locate potential hosts primarily through volatile chemicals emitted from the skin. Human odor consists of a complex mixture of compounds that varies between individuals because of genetics, diet, health status, and skin‑resident microbes. This variability creates distinct odor profiles that can either attract or deter bed bugs, influencing which people receive bites.

Bed bugs possess sensory receptors tuned to specific volatile organic compounds (VOCs). When a person’s odor contains high concentrations of attractants—such as lactic acid, ammonia, certain short‑chain fatty acids, and aldehydes—bed bugs exhibit increased locomotion toward the source and a higher likelihood of feeding. Conversely, the presence of repellent VOCs—like some long‑chain fatty acids, phenols, or microbial metabolites that produce a “off‑note” scent—reduces host‑seeking behavior.

The insects also use pheromones to amplify host cues. An aggregation pheromone released by fed bed bugs can draw conspecifics to a nearby host, creating a feedback loop that concentrates feeding on individuals already emitting strong attractant signals. This mechanism explains why multiple bites often cluster on the same person.

Key odor components influencing bed‑bug host selection:

• Attractants

  • Lactic acid
  • Ammonia
  • Isovaleric acid
  • 2‑methoxy‑3‑isobutylpyrazine
  • Certain aldehydes (e.g., hexanal)

• Repellents

  • Long‑chain fatty acids (e.g., palmitic acid)
  • Phenolic compounds
  • Specific bacterial metabolites (e.g., indole at high concentrations)

Research employing gas‑chromatography–mass spectrometry (GC‑MS) has identified consistent differences between the odor profiles of heavily bitten individuals and those rarely targeted. The data support a model in which personal chemical signatures, modulated by the skin microbiome, dictate the probability of a bite, while bed‑bug pheromonal communication intensifies the effect.

Body Temperature Variations

Bed bugs locate hosts primarily through thermal cues; the heat emitted by a human body creates a detectable gradient. Individuals with higher surface temperatures generate stronger gradients, making them more visible to the insects. Elevated temperature can result from fever, increased metabolic rate, or localized inflammation, and these conditions raise skin temperature by 1–2 °C above average levels.

Variations in basal body temperature also influence biting patterns. People with naturally higher resting temperatures—often due to age, hormonal factors, or chronic conditions—emit a steadier heat signal. Conversely, individuals with lower peripheral temperature, such as those with poor circulation or who sleep in cooler environments, produce weaker signals that may be overlooked by bed bugs.

Bed bugs possess infrared-sensitive receptors that respond to temperature differences as small as 0.1 °C. When a host’s skin temperature exceeds ambient room temperature by a noticeable margin, the insects orient their movement toward the heat source and initiate feeding. If the temperature differential falls below the detection threshold, the insects may continue searching without a bite.

Practical implications:

• Reducing skin temperature before sleep (e.g., cool shower, breathable bedding) can diminish the thermal gradient.
• Maintaining lower room temperature lowers overall heat contrast, decreasing host visibility.
• Managing fever or inflammatory conditions with appropriate medical treatment reduces localized temperature spikes.

Understanding how body‑temperature variation modulates host detection helps explain why some people receive more bites while others remain largely untouched.

Carbon Dioxide Production

Carbon dioxide released by a human body acts as a primary signal for bed‑bug host‑seeking. The insects detect CO₂ gradients with sensory organs on their antennae and move toward increasing concentrations. This chemotactic response explains why some individuals receive more bites than others.

Resting adults emit approximately 0.04 L of CO₂ per minute; vigorous activity can raise output to 0.2 L min⁻¹ or higher. The difference in emission rates creates distinct plumes that bed bugs can follow. Individuals with higher metabolic rates generate stronger plumes, making them more detectable.

Factors influencing CO₂ production include:

• Basal metabolic rate (elevated in larger bodies, males, and younger adults)
• Physical activity level (exercise, movement, fidgeting)
• Physiological conditions (fever, hyperthyroidism)
• Ambient temperature (warmer environments increase respiration)

When a person’s CO₂ plume exceeds the detection threshold of bed bugs, the insects are more likely to initiate probing and feeding. Conversely, low‑emitting individuals may remain below the threshold, reducing bite incidence.

Understanding CO₂ output provides a quantifiable metric for assessing susceptibility to bed‑bug bites. Monitoring or modifying factors that affect respiration can influence exposure risk.

Blood Type and Composition

Scientific Theories and Evidence

Scientific investigations attribute the selective feeding of Cimex lectularius on certain individuals to multiple physiological and biochemical factors. Evidence from controlled laboratory studies and field observations supports the following mechanisms:

• Skin microbiome composition – Analyses of bacterial communities on human skin reveal that individuals with higher concentrations of certain Staphylococcus and Corynebacterium species emit volatile compounds that attract bed bugs, while others produce fewer attractants.
• Blood group antigens – Epidemiological surveys indicate a higher incidence of bites among persons with blood type O compared with A, B, or AB, suggesting that surface antigens influence host detection.
• Thermal and carbon‑dioxide output – Infrared imaging shows that people with elevated basal metabolic rates generate stronger heat signatures and greater CO₂ flux, both of which serve as primary cues for host location.
• Cutaneous chemical signals – Gas chromatography–mass spectrometry identifies specific fatty acid derivatives and lactic acid concentrations that correlate with bite frequency; higher levels increase host attractiveness.
• Immune response variability – Immunological assays demonstrate that individuals with robust IgE-mediated reactions experience more pronounced bite lesions, potentially reflecting a feedback loop where heightened inflammation draws additional insects.
• Genetic predisposition – Genome‑wide association studies have linked polymorphisms in olfactory receptor genes to heightened sensitivity to bed‑bug kairomones, implicating inherited traits in bite susceptibility.

Collectively, these data delineate a multifactorial model: host selection results from an interplay of microbial emissions, biochemical markers, thermal cues, and genetic factors. Ongoing research employing metabolomic profiling and functional genomics aims to refine predictive markers and develop targeted repellents.

Individual Blood Characteristics

Bed bugs locate hosts through heat, carbon dioxide and skin odors, yet the likelihood of a bite depends on specific properties of a person’s blood. Blood composition varies among individuals, influencing the insect’s feeding preference and the skin’s reaction after a puncture.

Key blood traits that affect susceptibility include:

• Blood type – Certain studies show that type O blood attracts more hematophagous insects, while type A may be less appealing.
• Blood glucose level – Higher glucose concentrations increase the osmotic pressure of the blood, making it more nourishing for the bug and therefore more attractive.
• Hemoglobin concentration – Elevated hemoglobin provides a richer protein source, encouraging longer feeding periods.
• Blood pH – Slightly acidic blood can alter the chemical cues released through the skin, enhancing detection by the bug’s chemosensory organs.
• Presence of specific antigens – Some surface proteins act as chemical signals that insects can recognize, affecting their choice of host.

These physiological differences also shape the immune response to a bite. Individuals with heightened histamine release experience more pronounced swelling and itching, which may be misinterpreted as increased attractiveness, whereas low‑reactivity individuals show minimal visible signs despite being bitten.

In summary, variations in blood type, glucose, hemoglobin, pH, and antigenic profile create a biochemical landscape that either draws or deters bed bugs, while individual immune reactivity determines the observable aftermath of a feeding event.

Other Potential Influencers

Skin Thickness and Sensitivity

Bed bugs locate their hosts primarily through heat, carbon‑dioxide, and movement, yet the physical characteristics of human skin influence whether a bite occurs.

• Epidermal thickness varies across body regions and between individuals. Thicker stratum corneum layers impede the insect’s stylet penetration, increasing the likelihood that the bug aborts the feeding attempt.
• Dermal collagen density affects tissue rigidity. Higher collagen content provides additional resistance to the probing mouthparts, reducing successful blood extraction.

Sensory thresholds also determine bite incidence.

• Nerve fiber distribution differs among people; a lower density of nociceptors in the epidermis delays pain perception, allowing the bug to feed longer before the host becomes aware.
• Histamine release propensity varies genetically; individuals who mount a muted inflammatory response experience fewer visible welts, which may discourage further feeding by the insect due to reduced host cues.

Collectively, greater skin thickness and reduced sensory sensitivity create a less favorable environment for bed bugs to obtain a blood meal, explaining why some people attract bites while others remain largely untouched.

Allergic Reactions and Immune Responses

Bed bug feeding patterns depend heavily on individual immune characteristics. When a bite penetrates the skin, the insect injects saliva containing anticoagulants and proteins that trigger the host’s immune system. In some people, these salivary components are recognized as foreign, prompting a rapid inflammatory cascade that produces visible welts, itching, and swelling. Others experience minimal or no reaction because their immune system either does not recognize the proteins as threats or mounts a subdued response.

Key immunological factors that influence bite outcomes include:

• IgE‑mediated hypersensitivity – elevated specific IgE antibodies bind to salivary allergens, activating mast cells and releasing histamine, which amplifies redness and itch.
• Th2‑dominant cytokine profile – a skewed Th2 response favors antibody production and eosinophil recruitment, intensifying skin inflammation.
• Skin barrier integrity – compromised epidermal protection permits easier entry of salivary proteins, increasing antigen exposure.
• Previous sensitization – prior encounters with bed bug saliva can prime the immune system, leading to quicker and stronger reactions on subsequent bites.

Conversely, individuals with low IgE levels, a balanced Th1/Th2 response, or robust skin barriers often exhibit negligible symptoms, allowing the bite to go unnoticed. The variability in allergic and immune responses therefore explains why some hosts display pronounced reactions while others appear unaffected.

Genetic Predisposition

Genetic variation shapes individual susceptibility to bed‑bug feeding. Specific alleles alter skin secretions, blood composition, and immune signaling, creating distinct chemical cues that insects detect.

• Certain HLA class II genotypes correlate with heightened bite incidence, suggesting immune‑mediated modulation of odorant profiles.
• Polymorphisms in odorant‑receptor genes affect perception of kairomones; carriers of particular variants emit higher concentrations of attractive volatiles such as aldehydes and fatty acids.
• Blood‑type genes influence plasma protein levels; type O individuals often present lower concentrations of certain glycoproteins that deter feeding, while type A subjects may produce attractant molecules in greater amounts.
• Genes governing skin microbiota composition indirectly affect volatile organic compound production; variants that favor colonization by Corynebacterium and Staphylococcus species enhance the release of compounds known to lure hematophagous insects.

These genetic factors operate together, creating a biochemical landscape that either invites or repels bed bugs. Population studies confirm that families sharing susceptibility alleles exhibit similar bite patterns, reinforcing the hereditary component of the phenomenon.