What is biting me at night?

Overnight bites narrow to a short list: bed bugs, fleas, mosquitoes, an occasional spider, scabies mites, or a skin condition that is not a bite. The pattern and the location on your body separate them faster than anything else.

Start with the pattern

• Lines or zigzags of three or more, on skin left uncovered by bedding — bed bugs.
• Below the knee, clustered, with a pet in the house — fleas.
• Random single bumps anywhere exposed, fading in a day or two — mosquitoes.
• Symmetrical, in finger webs, wrists and waistline, itch unbearable at night, others in the household itching too — scabies.
• One painful bite with immediate stinging, on the neck or arm — possibly a yellow sac spider.
• Itchy, symmetrical, no visible punctures, worse under tight clothing — often not bites at all.

Check the bed, not just the skin

Bed bug evidence beats bite interpretation every time. Strip the bed and look at the mattress seams, the piping, the underside of the frame and the headboard for: small dark ink-like spots, shed skins, or live insects the size and shape of an apple pip. A torch and ten minutes settles it.

When nobody else is bitten

That proves nothing. Roughly a third of people develop no visible reaction to bed bug bites, and reaction strength varies enormously between individuals sharing a bed.

When it is not bites

Several conditions mimic bites well enough to fool most people: hives, dermatitis herpetiformis, folliculitis, and simple contact dermatitis from a new detergent. The clues are symmetry, absence of a central puncture, and a pattern that follows clothing rather than exposure.

If you have searched the bed thoroughly, treated pets, and bites keep appearing with no insect ever found, a dermatology opinion is more useful than another round of insecticide.

What to do tonight

Wash bedding hot and tumble dry, vacuum the bed frame, and take photographs of the bites in daylight — timing and progression over several days is exactly what a clinician or a bite assessment needs.