I also heard a skeptical podcaster mention that sometimes there could be bone shards in the food. Thank you for the information.
The main reason for asking was the skin thing. I had heard in the past a change in diet could help. I'd like to try things before committing to going to a vet. It could be expensive. Could a good shampoo and wash help? If it's fleas a flea shampoo should help.
Fleas should be pretty easy to identify. Just check your pup out. Sit down with him and give him a good pet and scratch, and just check his fur. Spread the fur apart and look at his skin for rashes, fleas, or "flea-dirt" which is just a mix of flea poo and blood. It'll be like black specs. Fleas are easy to identify because they're living bugs. So you'll see them move and even jump (yikes).
If you had fleas, I'd suspect you'd know it though.. They bite humans too and if they go un-contested for too long you'll end up with them attacking you as well and you'll be covered in bites/bumps yourself, generally on the arms and lower legs.
Dogs definitely can have allergies, and food can cause those allergies to flare. Switching food can help. Try a small bag of another brand, or another formula. There are foods specifically marketed towards allergies. The one thing my partner had said is that the "Grain-free" branding is likely a gimmick and none of the vets she knows recommend it. Grains on their own aren't really bad for dogs, and instead are usually the scape-goat for low-quality brands that use loads of grains purely as filler.
Lastly, dogs are creatures are habit, and when you change foods you may notice your dog is hesitant to eat, or perhaps ends up with loose stools or an upset tummy. This is pretty normal at first and shouldn't be immediate cause for concern. Something worthy of taking note of, but not getting worried unless it's persistent.