A dog can definitely have an allergy to human dander. In fact, it's probably more common that you think. Many kinds of allergies are very common in dogs. These allergies usually manifest as skin problems.
Owners don't always find out what their dogs are actually allergic to. Vets often treat dogs symptomatically when it's a not yet a chronic skin problem (or when owners do not wish to have allergy testing done). Some dogs respond to the treatment of symptoms, so we don't necessarily need to find out what they are allergic to.
It's fair to assume that there are many dogs out there with human allergies; they just don't get diagnosed. In reality, many dogs with skin issues are allergic to multiple substances.
When humans are allergic to dogs, they may sneeze and sniffle. Others may break out in hives. When dogs are allergic to human dander (and many other things), they tend to have gradually progressive skin issues. The reaction does not usually happen all at once (the way people start sneezing or breaking out). Instead, it usually starts with mild skin irritation and itching. Over time, the skin irritation gets worse, the itching gets worse and the scratching further irritates the skin. Irritation may cause the skin to become infected (bacterial or fungal/yeast). It's kind of a vicious cycle.
Stories of dogs allergic to humans have even been in the news.
Is My Dog Allergic to Me?
For starters, if your dog is itchy or has an apparent skin problem, go to your veterinarian. Once the immediate skin issue is diagnosed and treated, your vet can talk to you about options. If an allergy is suspected, your allergic dog might actually have multiple allergies. Allergy testing is the only way to know for sure what your dog is allergic to. Some vets will offer a blood test to check for allergies. However, veterinary dermatologists agree that blood testing for allergies simply is not accurate. Skin testing (intradermal allergy testing) for allergies is the way to go. With skin testing, the tiny, controlled allergic reactions can be seen in real time and are quite obvious to the trained eye.
Can Dogs With Human Allergies Be Treated?
There is hope for dogs allergic to humans, and it's not living in isolation from people! Once a definitive diagnosis is made, a customized allergy serum will be developed. This serum is then given to the dog as injections over a period of time (as prescribed by the vet). Other medications may be needed, and management of allergies is often a lifelong process. However, many dogs can live a comfortable, happy life despite these allergies.