Hypersensitivity to Bug Bites
For the average person, a bug bite usually stops itching within a few days. However, some people are extra sensitive to certain insect bites, causing a more serious problem, insect bite-induced hypersensitivity reaction. The bite spot becomes intensely itchy, inflamed and swollen. A spreading rash forms and the affected lesions fill with fluid. Scratching can break open the bumps and allow bacteria to enter the wound, leading to a secondary bacterial infection.
It isn't known how many people are affected by insect bite-induced hypersensitivity reaction. One study found the problem accounts for about 5 percent of visits to a specialized dermatology clinic. Bernard Cohen, M.D., Pediatric Dermatologist with Johns Hopkins Children's Center in Baltimore, says the reaction is caused by sensitivity to proteins in the insect saliva. A person needs to be bitten several times to build sensitivity, so the symptoms are rare in those under two. Peak prevalence is in children between 2 and 10. In most cases, Cohen says, people eventually develop a tolerance to the bite proteins. Thus, insect bite-induced hypersensitivity reaction is much less common in adults.
Diagnosing the Problem
Cohen says it is sometimes difficult to pinpoint the cause of intensely itchy areas of skin. The symptoms may not be associated with insect bites, especially when patients haven't spent a lot of time outside or been knowingly exposed to biting insects.
Cohen recommends using the mnemonic word, "SCRATCH" to aid in diagnosis of suspected reaction to insect bites:
S stands for symmetrical distribution of the lesions, meaning they are typically found over exposed (uncovered) surfaces of the body.
C is for clusters or crops. Insect bites tend to occur in groups, which reflect continual feeding, or as Cohen calls it, "breakfast, lunch and dinner." This is especially true for flea bites and bed bug bites. The clusters tend to recur when the patient is exposed to the source of the insects (like a cat's litter box).
R means "Rover" not required. Homes without pets can still have fleas because the insects can be carried into the home on clothing or other items. In some cases, former pet owners aren't aware of flea infestation until an animal is gone and the insects begin to seek an alternate host for their meals.
A refers to age-specific. While insect bite-induced hypersensitivity reaction can occur at any age, it is most common among those 2 to 10.
T stands for target lesion. These are the very characteristic bumps associated with insect bites - beginning as a red bump, and then developing into a blister. The blisters eventually scab and heal. The "T" also stands for time, because the lesions recur in a chronic pattern.
C refers to the confused physician and parent. The physician may have a hard time getting the parents to understand the cause of the symptoms, and that the solution (i.e., eradication of fleas and bedbugs) may be costly and difficult. Parents often disbelieve the symptoms are associated with bug bites, or that the home may have fleas or bedbugs.
H is for households with a single affected family member. Cohen says, typically, only one member of a household is hypersensitive to the bug bites, leading many parents (and sometimes physicians) to question the diagnosis. However, he explains that not everyone reacts the same way to bug bites because everyone has different threshold of sensitization. Younger children are also more likely to be affected than older ones, who typically develop a level of tolerance to the bites.
Treating/Preventing Bug Bites
Cohen says there's not a lot that can be done for itchy insect bites. Sometimes application of cool compresses or calamine lotion is helpful. For significant itch, topical steroids may be used. He discourages using a significant amount of topical antihistamine for a child because insect bite hypersensitivity isn't a histamine-induced reaction, and too much of the active drug can be absorbed into their body, potentially leading to an overdose. If the skin appears very red and swollen, or the child has signs of infection, see a doctor for treatment.
It's very difficult to avoid insect bites. Staying indoors won't keep people away from fleas, bedbugs and mosquitoes that fly in through an open door or window. Cohen recommends taking precautions when outdoors. Use an insect repellant with DEET. The American Academy of Pediatrics says products containing up to a 30 percent concentration of DEET can be used for children. Repellant can also be sprayed on clothing. Avoid using sunscreen and skin care products that are scented (the smell may attract insects). Wear long sleeves and long pants, especially in wooded and wetter areas, where insects are more common. If you have a pet, talk to your veterinarian about flea control products.
Research compiled and edited by Barbara J. Fister
American Academy of Pediatrics, http://www.healthychildren.org/English/tips-tools/Symptom-Checker/Pages/Insect-Bites.aspx
American Mosquito Control Association, http://www.mosquito.org
Food and Drug Administration, http://www.fda.gov/downloads/ForConsumers/ConsumerUpdates/UCM225621.pdf