There are many possible reasons for a dog to be losing hair. Some of these problems can be very serious, so it's important to get to the bottom of the problem. Hypothyroidism is one common cause of hair loss in dogs, which is very easily treated with inexpensive medication, and monitored with a blood test. With treatment, it does not affect the dog's life expectancy. On the other hand, sarcoptic mange (scabies) and ringworm are two causes of hair loss that can be contagious to people and other animals. Children are especially susceptible.
Examine your dog to find out if it is simply shedding excessively or actually suffering alopecia (hair loss). Shedding is a normal phenomenon and can be very heavy at certain times of the year. Female dogs will lose their hair by very heavy shedding (called "blowing the coat") after having puppies and nursing them. Generally, shedding involves hair falling out, but there will be no apparent loss of hair on the dog's body because the hair is shedding while new hair is growing in. In the case of nursing mother dogs, there is noticeable hair loss and the hair will have a dull, dry look and feel. But there are no bald spots or sores and the hair loss is the same over the entire body in all types of shedding. Sometimes excessive shedding is caused by poor diet, stress or living quarters that are too warm.
Determine if the hair is falling out on its own or if the dog is scratching so much that it causes the hair to fall out. If the dog is scratching a lot, has sores or scratches on its skin or licks its fur a lot, it's very likely that the hair is falling out because of the scratching. If you don't actually see the dog scratching and licking a lot, but notice brownish stains on its paws, tail or other parts of the body, then the dog is licking at those parts when you aren't looking.
Provide a high-quality dog food, with high levels of fatty acids. Fatty acids are essential for a healthy coat and skin. Switch gradually to the new food by adding more and more of the new food while reducing the amount of the old food over a two to four week period.
Brush your dog daily to help control shedding. Use a dog brush that is recommended for your dog's type of hair. This information is usually written on the label, but you can also ask a groomer, veterinarian or pet shop clerk for advice. Some dogs enjoy a vacuum attachment that allows you to vacuum the loose hair, and this is very good for the heavy shedding that some breeds experience in the spring and winter. These are available in pet stores or online, but shouldn't be used if your dog is very frightened by the vacuum.
Check your dog for fleas, especially if the dog is scratching or licking a lot. Use a flea comb to comb through the hair in good light, looking for fleas. Alternatively, put your dog on a light-coloured table top or hard floor, and rub gently but vigorously on the dog's fur. If you don't have a light-coloured surface for your dog to stand on, just put a white sheet or white paper towels on the floor under its belly. After you've rubbed its fur, look on the surface for tiny black dots. Use a damp tissue to smear the dots. If you see a streak of red, the black dots are flea dirt (flea excrement), so you know your dog has fleas even though you may not see them.
Apply high-quality flea drops directly onto the dog's skin, between the shoulder blades if you found evidence of fleas. Follow the manufacturer's directions carefully. Flea collars, powders and shampoos offer little help compared to the flea drops, which are often called spot-ons. If your dog continues scratching and losing hair, it must be sees by a veterinarian as it may have flea bite allergy, which will not resolve on its own for several weeks. By then your dog could likely develop a skin infection as well.
Take your dog to the veterinarian to rule out any serious health problems. There are many health problems, both minor and major, that can cause hair loss. Your veterinarian will have to give the dog a careful physical examination, and other diagnostic tests may be needed.
If you are bathing your dog more often than once or twice a week, reduce the baths to no more than once a week. Use a very mild dog shampoo, labelled hypoallergenic.
Some of the more common problems that cause hair loss in dogs can be contagious to other dogs or even to people, especially children, so it is imperative that the dog be seen by a veterinarian.