It might be a combination of food and seasonal allergies. The food/biscuits might be a slight problem but then added to the seasonal allergies, the allergies become major. Arnie has allergies and he rarely gets treats because of this and his kibble dog food is his treat.
Does your dog also have a rash on his stomach area or the inner part of his rear legs? Arnie usually starts off with this and then if he is biting his feet I know the allergies are bad. He has not had this for a few years though! I would clean the area and this would help tremendously. Allergies are difficult to diagnose.
The allergy season here in OH has been extended because of the crazy weather. If you have leaves on the ground that are/were wet, there could be mold, fungi, etc. on them and your dog is getting it on his paws.