Several vitamin deficiencies can cause hair loss in dogs, but the most common culprits are vitamin A, vitamin E, B-complex vitamins (especially biotin and niacin), and the mineral zinc. If your dog is losing fur in patches, developing a dull coat, or showing flaky skin alongside thinning hair, a nutritional gap is one of the first things worth investigating.
Vitamin A Deficiency
Vitamin A is essential for skin cell turnover and the health of hair follicles. When a dog doesn’t get enough, the skin becomes dry and thickened, and the coat turns dull and brittle. Over time, hair starts to thin or fall out, often with flaking or scaly patches underneath. Cocker Spaniels and other spaniel breeds are particularly prone to a condition called vitamin A responsive dermatosis, which causes red, raised plaques with crusty buildup around the hair follicles, typically on the belly and chest. These lesions can look similar to a skin infection, which is why they’re sometimes misdiagnosed.
The flip side matters too: giving a dog too much vitamin A is also dangerous. The safe upper limit for dogs is roughly 100 times the minimum requirement. Below that threshold, excess vitamin A accumulates in the liver and can cause peeling skin, nausea, weakness, and in severe cases, seizures. This is most likely to happen when dogs regularly eat human vitamin supplements or liver-heavy homemade diets. The standard minimum requirement for adult dogs is 5,000 IU per kilogram of food (on a dry matter basis), and most commercial dog foods meet or exceed this.
B Vitamins: Biotin, Niacin, and Others
The B-vitamin family plays a collective role in skin and coat health, but a few members stand out when it comes to hair loss.
Biotin (B7) is probably the most widely recognized nutrient for coat quality. It helps build keratin, the structural protein in hair and nails. Dogs deficient in biotin develop a dry, thinning coat, often with crusty skin around the face and eyes. Raw egg whites are a classic cause of biotin deficiency because they contain a protein called avidin that blocks biotin absorption. Cooking the eggs eliminates this problem.
Niacin (B3) supports skin health and helps control inflammation. A deficiency can lead to dermatitis, digestive upset, and general lethargy. In dogs, niacin deficiency tends to show up as inflamed, irritated skin that can progress to hair loss if left unaddressed. Unlike many animals, dogs cannot efficiently convert the amino acid tryptophan into niacin, so they depend more heavily on getting it directly from food. The minimum recommended level in dog food is 13.6 mg per kilogram of diet.
Pantothenic acid (B5) contributes to energy metabolism and hormone production. While severe B5 deficiency is uncommon in dogs eating commercial diets, an insufficient intake can weaken the immune system and slow wound healing, both of which indirectly affect coat condition. The recommended minimum is 12 mg per kilogram of food.
Riboflavin (B2) deficiency, though rare, can also cause dry, flaky skin and hair loss. Most quality commercial dog foods contain adequate levels of all B vitamins, so deficiencies are more common in dogs on restrictive, homemade, or poorly formulated diets.
Vitamin E Deficiency
Vitamin E is the body’s primary fat-soluble antioxidant. It protects cell membranes from damage, reduces inflammation, and helps maintain the structural integrity of skin cells. When a dog is low in vitamin E, skin becomes more vulnerable to oxidative stress, which can lead to dryness, itching, and eventually hair loss. Veterinarians frequently recommend vitamin E supplementation for dogs with coat and skin problems, including allergic dermatitis and certain autoimmune skin conditions.
The minimum recommended level for adult dogs is 50 IU per kilogram of food. Dogs eating diets high in polyunsaturated fats (like fish oil) need more vitamin E because those fats increase the body’s demand for antioxidant protection. If you’re adding fish oil to your dog’s food for coat health, pairing it with adequate vitamin E is important to avoid creating a new problem while solving another.
Zinc Deficiency and How It Differs
Zinc isn’t a vitamin, but it’s worth mentioning because zinc-responsive dermatosis is one of the most common nutritional causes of hair loss in dogs and is easily confused with vitamin deficiencies. Dogs with zinc deficiency develop red patches covered with thick, yellowish crusts, most often on the face (around the eyes, mouth, and ears) and on pressure points like the elbows and hocks. The pattern is distinctive: the crusting is heavy and waxy, and the hair loss clusters around those specific areas.
Two types of dogs are especially vulnerable. Arctic and northern breeds like Siberian Huskies and Alaskan Malamutes have a genetic tendency to absorb zinc poorly, even when their diet contains enough of it. Rapidly growing large-breed puppies can also develop zinc deficiency if their food is over-supplemented with calcium or phytate-heavy grains, both of which interfere with zinc absorption.
Why Deficiencies Happen on Commercial Diets
Most dogs eating a complete and balanced commercial food that meets AAFCO nutrient profiles will get adequate vitamins and minerals. Deficiencies are far more likely in specific situations: homemade diets that haven’t been formulated by a veterinary nutritionist, raw diets that rely too heavily on one protein source, or dogs with underlying conditions that impair nutrient absorption (chronic digestive disease, pancreatic insufficiency, or intestinal parasites).
Some dogs can also eat a nutritionally complete diet and still develop skin and coat problems because of poor absorption rather than poor intake. Inflammatory bowel conditions, for instance, can prevent the gut from pulling enough zinc or B vitamins out of food. In these cases, the deficiency is a secondary problem, and treating the underlying condition matters more than simply adding supplements.
Identifying the Cause
Hair loss from nutritional deficiency tends to look different from other causes. It’s usually symmetrical (affecting both sides of the body similarly), gradual, and accompanied by changes in skin quality: dryness, flaking, thickening, or crusting. The coat often becomes dull and brittle before actual bald patches appear. If your dog’s hair loss is patchy and asymmetrical, or if it came on suddenly, the cause is more likely to be hormonal (thyroid disease, Cushing’s disease), parasitic (mange, fleas), or infectious (ringworm, bacterial skin infections).
A veterinarian can run blood tests to check levels of specific nutrients, along with thyroid and other hormone panels, to narrow down the cause. Skin scrapings and fungal cultures can rule out parasites and infections. If a nutritional deficiency is confirmed, targeted supplementation under veterinary guidance usually produces visible improvement in coat quality within four to six weeks, though full regrowth can take several months depending on the severity.