Allergies are the result of an overactive immune system that releases histamines in its' effort to rid the body of foreign proteins from pollen, dust mites, trees, grass, household dust, dander, and many other materials.
Atopic allergies is believed to have a genetic component so you will want to ask your Breeder if they have seen any skin issues, if so what was the condition, how did it affect the dog, how is it treated and often has this problem been seen in dogs from their lines.
Some people may talk about a dog 2 or 3 generations back that used to itch when it was on certain grasses or who reacts to chicken, these are allergies and need to be considered when looking at potential offspring.
There are legitimate hormone related skin problems i.e. a Bitch may have skin issues occur around her heat cycle and then clear up afterwards etc.
Thyroid problems can also be a cause of skin issues.
There is some evidence that already sensitive dogs can be affected by allergies due to vaccination, your Breeder will be able to tell you if there is a vaccination sensitivity in their line.
Some people may deny the genetic component to allergic skin disease as perhaps only one puppy in the litter has allergies, however genetics doesn't affect every offspring just like one child in a family of 6 may need glasses and the others do not.
Allergies can be an expensive and heartbreaking condition, some dogs have minor seasonal flares ups where others suffer all year round and have to be on medication to have quality of life.
Skin Allergies/Skin Conditions are more easily seen on Harlequins as you can see the pink skin through the white hair, some believe Harlequins are more at risk of skin issues due to the pigmentation.
Dogs with skin issues can also suffer from digestion issues their whole lives and may require a supplementation of digestive enzymes.
Avoid purchasing a dog whose parents have noticeable skin problems such as pink/red skin, dull brittle coat, skin scabs, smell of yeast (smell like corn chips), scratched skin from where the dog has been scratching alot, hair loss etc, and avoid purchasing a puppy that has noticeably pink skin.
Allergic Skin Disease can start as young as in baby puppies and in some cases not until a dog is 2 years of age.
There are different forms of testing available as well as desensitising injections that have varied results.
An ethical Breeder will not breed known allergic dogs.