The most common feline allergies are tied to flea and environmental items (chemicals in carpet, exhaust, etc). Rarely, though, cats can develop pruritus (extreme itchiness) from food allergies.
Common food allergies for cats include beef, dairy, fish, lamb and poultry. Rarely, but still occurring, are allergies to soy, gluten, or other non-meat products present. Allergies like these are more common in dogs, however, and these ingredients are less prevalent in cat foods.
Rise in feline pruritus due to food allergies
Nationally, veterinarians are reporting a rise in pruritus in felines due to food allergies, but the rise is nowhere near as fast as is the similar allergic rise in humans. Environmental causes are the most prevalent and hardest to pinpoint for cats and fleas are usually the easiest. Food allergies require relatively time-intensive testing with special diets to determine the allergen and most cat owners cannot pay the expense for this testing, so it often goes undone.
A current study in New Jersey is surveying the prevalence of allergies of various types in cats nationally and is expected to conclude this summer.