Lots of mosquitoes/gnats around this year probably because they spend the first half of their life as larvae in water. So the more ponds and puddles there are the better they breed. Get rid of any standing water in your garden e.g. buckets with rainwater standing in them. It only takes a cupful and they are away.
These insects are attracted by smell - we all have our unique pongs, partly driven by genes and partly by the biome of friendly bacteria that live on or in our bodies. Biting insects attracted to the smell of humans (or whatever is their meal of choice) so not unreasonable to suspect that some smell more alluring than others. My DH is more attractive to mozzies than i am, but sandflies in NZ (completely different species) love me as much.
Mozzies bite after dark. Hence mosquito nets. Windows closed after dark maybe? and check bedroom for lurkers?
But other things - like horseflies - hunt by day.
It is possible though that the red bites on one person and not on another are because although they have both been bitten one persons immune system is reacting more strongly and producing more histamine than the other one. It is the histamine that makes you itch.
Anthisan antihistamine is the drug of choice in our house.
A couple of times I have been so badly bitten that I could only sleep by taking one of DH's antihistamine hayfever pills, which damped them down successfully.