How many food allergies can be detected by a skin allergy test?

Be cautious: Skin testing is a minor adjunct to the clinical history. Some people test positive for lots of different foods and restrict themselves unnecessarily. The same applies for bloodwork. I would be very cautious before basing decisions on these tests. Your allergist will tell you the same.

Unlimited, but...: There are many (>100) foods available, but as it turns out, the vast majority of patients are allergic to a limited number. The "top 8" foods are cow's milk, hen's egg, wheat, soy, peanuts, tree nuts, fish and shellfish. Screening for dozens of random foods rarely is helpful and may lead to an overly restricted diet. Review your story with the ordering provider and tailor accordingly.