Two main things, The amount of venom that goes in has the biggest effect. When you catch the bee early in the sting and get the stinger out,"along with the venom sac" you don't get as much venom in you.
After being stung several times at different times over a month or two, I still swell a lot "if" the venom is allowed to go in.The first stings will have a greater effect, than the ones later, "again", depending on the amount of venom you get. I am speaking "only of itchy, redness and swelling.
ANYONE, who has reactions other than normal itchy, redness, and swelling, SHOULD, be careful.
doak