Bed bug bites are the same as mosquito bites in appearance, hence making them indistinguishable based on the appearance alone.
A potential way of trying to tell the difference could be, watching the welts closely, or looking out for patterns, or just waiting for further symptoms to appear or existing ones to vanish.
Mosquito bites are usually isolated or singularly located, and the welts almost always itch, but rarely more than for an hour or two.
Mosquito bites are usually harmless (unless they’re particularly carrying certain diseases) and the marks vanish shortly after the itching disappears.
Contrary to these mosquito bites, bed bug bites mostly appear in clusters, typically in a vertical line of 3, commonly referred to as the ‘breakfast, lunch and dinner’ formation.
Bed bug bite welts may or may not itch, though the ones that itch can itch terribly, with the itch lasting as long as several days sometimes, getting worse as time passes.
Bed bug bites often cause small raised bumps, while a mosquito bite may look like a small, flat pimple. Mosquito bites are instantly realized, and symptoms vanish shortly thereafter, whereas, bed bug symptoms typically don’t show up for a few days after exposure.
This is due to what is called the ‘lag time’, which is the difference between the actual bites and the onset of symptoms.
The lag time for bed bug bites can be as much as 9 days, less for more bites. Bed bugs are not known to carry or transmit human diseases.
Climatic conditions also play a major role in helping the bitten determine the cause of the bite. Extreme winters or extreme heat, for example, wipe out most of the mosquito population, while bed bugs remain unaffected.
So this could be some help in telling the difference between the two bites. There really are no sprays or lotions to help one avoid getting bed bug bites if there already is an infestation.
While there are several mosquito repellents that can be used to ward off mosquitoes, which can be another factor helpful in determining what caused the bite, by considering if any repellant was used or not.
There are very few ways of determining for sure, what could have caused the bite. The most common hazard in both though is the chance of infection by scratching the open wound, which should be avoided, especially in the absence of a doctor.