Humans can use flea collars to keep fleas and ticks away from them.
However if a human uses a flea collar they do so at their own risk as the chemicals that are used in flea collars can be toxic to humans.
The chemicals in flea collars that can be toxic to humans can be absorbed into the blood through the humans skin so it's not recommended to wear a flea collar as a human.
However when I was out in the woods I put a flea collar on both my wrists before to prevent ticks from getting onto my wrists.
I would reach down for something or go through some brush and then ticks would get onto my wrists or arms.
But when wore a flea collar on those arms I no longer had any problems with ticks getting on there.
I haven't gotten sick from it but I didn't wear the flea collars on my wrists all the time but only when out in the woods.
And I made sure to wash my arms and wrists off really good after removing the flea and tick collar.