Mark Mandell - Gone Round In New Jersey
Walnut is a "sensitizer" meaning that the more exposure you have, the more it will effect you. That's different from an "allergy" but given time, the effect may be the same. I know at least one famous woodturner who, after working fresh-cut walnut for years, now finds himself in the position of the stuff being able to kill him with minimal exposure. Walnut's juglone protean extractive may be the primary culprit, but other extractives in the dust may also compound the effect.
Woodturners are especially susceptible due to their fondness for fresh-cut wet wood that has all the "bad" stuff intact.