Not your health, but, it can effect you emotionally. They are not a pretty thing and personally, I don't think they should ever be given for any reason. I, too, agree with all the above answers, they have a lot of merit.
Not your health, your self respect maybe. Anyone who sees it will laugh and make fun of you. Why would your boyfriend want that for you? Ask yourself why a boy would go to all that trouble to leave a mark like that on your neck. Think about it for a while. If you can't find an answer, then think about why would you ever give one of those to someone else? I let that happen to me once and only once. Try giving your boyfriend a hickey and see how he likes it. Seriously, watch his reaction. That will be a wake up call for you. Ah, to be young again. This was a learning experience for you, that's all. Learn from it.
if you get too many it could cause to skin cancer, im not 100% sure if this is true, but my mum always used to have a go at me if i got one because she said they can give you skin cancer so please becareful
A hickey will not damage your health. But it may cause you some self-conscious issues. You may want to keep it covered until it goes away, or apply make-up to hide it.
they aint good things to have not only do they look ugly and coomon it is not a good thing to allow someone to do when he is sucking your neck he is drawing the blood to the surface,not life threatening,but best to tell him you dont like them