My Fell x Border terrier gets itchy during the summer, apparently caused by some kind of mite.
A hose down after a walk helps, as does a good diet. Many dog fuds contain wheat of the poorest quality which does them or their skin no favours at all. We feed ours “Lily’s Kitchen”. Pricey, but stuffed full of good things, and they they love it.
There is a supplement available for ponies and dogs called “ultimate oil” which works wonders for itchy skin.
http://www.kmeliteproducts.co.uk/Pet/km-elite-canine-ultimate-oil-500ml
Half a teaspoon in their nosh and after a few weeks they’re cushtie, and a lot hairier!
As a last resort, there’s a tablet from your vet called Apoquel. Pricey but fewer side effects than steroids.