You have to put on protections before you go cursing.
Cursing opens you up to spiritual energies. This type of magick work is full-contact. Like any full-contact sport, you want to have protective gear on so you don’t get messed up when other beings hit back. Which they will, depending on who you curse - or who’s observing and chooses to jump in on the action.
Understand that many people ALREADY have spirits possessing them - the average person is already possessed by at least one of the 7 Deadly Sins, and the spirits that rule them.
This effectively makes them experienced magicians, even though they don’t have the experience - the spirit has experience in using them.
So cursing someone who indulges in their vices becomes a mini tug-of-war, you vs the spirit within them.
Put wards and protections around yourself before you go cursing.
Do cleansing baths and use spiritual hygiene before summoning and sending curse agents. Otherwise, they cling onto you.
Realize that curses are most effectively sent using necromancy and elementaries, larvae which cling to human life. This is dangerous work and shouldn’t be done by novices.
Crawl before you walk when you do this stuff. It’s easy to fuck yourself up unawares due to lack of knowledge.