Blood worms can cause an itchy reaction. The worst I have heard about is someone feeding freeze dried bloodworms, then sort of just dusting off their hands, then touching their eye. Had to go to the doctor.
To test this put some blood worms in a jar of water, make it pretty concentrated, and stick your hand in it.
If you feed blood worms in any form (frozen, freeze dried or as a component in a blended food) STOP.
Wear gloves until you have done several very thorough cleanings, vacuum the substrate the best you can, filter cleanings... and gotten rid of the blood worm remnants.
Once you are sure the tank is clean, try it bare handed again.
If the problem does not come back, it might have been the blood worms.
If this is not the answer, then in turn eliminate one at a time everything else you use in the tank. (put some of each item, one at a time, in a jar of water and stick your hand in)
Protein based things can cause allergies, other things can be irritants. Even if you do not normally react to much there seems to be something in the aquarium. By isolating each item in a separate jar you will highly likely figure out what is the problem and then you can eliminate it from the tank.