Dog gets itchy skin because of few reasons and here are some of them:
Ticks, hookworm, tapeworm etc can get inside the dogs body and the dog will start itching. In case of ticks the dog will start itching because the ticks will sucks the dog's blood and that creates itching sensation.
You will be able to see the ticks and if you see them remove it with a tweezer. If you cannot identify what's causing the itching then immediately take the dog to a veterinarian.
The dog can get infection because of various reasons like eating contaminated food, infection from a dog bite, Infection from germs etc and that can create irritation in the dog body and because of it the dog will start itching.
However infections should not be taken lightly and an immediate checkup is necessary. If you cannot take the dog to a veterinary then atleast tell the symptoms to a vet and they will give the right treatment.
3. Skin Disease
Dog can have skin disease. The skin disease can start from mild infection and then will start to spread.
It's very important to treat the dog on time or else the dog may lose all of its hair and can eventually die. If you see discoloration, red patches around the dog's body then get the dog treated.
These are some of the early signs of an skin disease. It may not spread immediately but overtime it will become problematic.
The dog will start itching when the dog feels irritation in its skin and will show sign of discomfort.
4. Oily And Spicy Food
Dog will start losing its hair if you feed them oily and spicy food. These foods are not made for dogs.
They may eat with pleasure but the adverse effects are very bad. Itching, low hair volume, lusterless hair are some of the sign. Avoid giving as much oily and spicy food to your dog.