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An allergic reaction to antler would be extremely unlikely.
It may be from irritation not an actual allergic reaction. The fine particles from grinding can have tiny sharp points. That would be similar to the reaction from sanding fiberglass.
Is the antler from a harvested from a deer someone shot recently? That could have bacteria on it in the velvet, blood, and base bone that may cause a skin infection/irritation.
To lessen skin irritation from grinding wood, metal, bone, ivory, fiberglass, etc. Dust off your hands and arms gently or vacuum them, rinse well with running cool or warm water (not hot water), then wash with a mild detergent like Dawn. Try not to rub hard in the washing. Rinse well before drying.
It is also possible that the cause is from something unrelated to the knife work. Mild eczema in older folks often appears as itchy skin on the arms and especially between the fingers.
As a fellow septuagenarian, I can sympathize with you about the itches we get all the time. I have found Cera-V to be one of the best treatments for the "itchies". The other advice is DON'T SCRATCH THE ITCH ... gently rub in some cream.