My DD has a topical reaction to eggplant. Not common, not rare, but she also has no other allergies at all, and none to the other foods in this group usually known for being allergens.

So yes, it could be the Farex. But as others have said, I would also be looking at your washing powder in particular, or any other cleaning products you ise in the house on a regular basis.

Good luck and hope you find your answers