Dog losing hair: is the food to blame and how long until new hair grows back

Take a 30 kg Labrador, five years old, neutered. In spring his hair is on the floor, on the sofas and on black trousers. In winter the owners cut his portion because he started gaining weight, and now they are searching online for an “anti-shedding” food.

On a complete food, hair rarely falls out because of nutrition: nutrient deficiencies have become rare precisely thanks to such foods (Watson, J Nutr, 1998). Food really becomes the cause in one scenario, when there is little protein per calorie and the portion has been cut. A 30 kg Labrador on a cut portion of 897 kcal of a food with 20% protein gets 48 g of protein, or 76% of the FEDIAF minimum, while on a normal portion the same food provides 121%. Below is the full calculation and the time after which you can judge the result.

See also: Dandruff in dogs

How much hair should a dog normally lose?

Heavier shedding in spring and autumn is normal, and it shows at the follicle level: in nine beagles, peaks of hair loss during brushing fell exactly in spring and autumn, together with peaks of follicles in the telogen phase (Al-Bagdadi et al., Am J Vet Res, 1977).

Telogen is the resting phase of the hair follicle, when the hair no longer grows and is held loosely in the skin.

In Labradors, over 80% of hairs were in telogen in any season (Diaz et al., 2004), and beagles under one year had 10% fewer such follicles than adults. A dog always has a stock of hairs ready to fall out, which is why owners often mistake the first adult shed for an illness.

None of these studies measured how many weeks seasonal shedding lasts, and articles quoting “2–3”, “2–4” and “4–6 weeks” give no sources.

Harder is telling this normal shedding apart from a case where the food is to blame.

Can food be the reason a dog is losing hair?

Food is rarely the cause, because nutrient deficiencies stopped being common precisely because dogs are fed complete foods.

“Nutritional deficiencies are now uncommon,” Watson wrote in the Journal of Nutrition in 1998, reviewing nutrition and skin disease.

A 1988 case series shows what a real “food is to blame” case looks like: 13 dogs with crusting dermatosis, all on cheap corn-and-wheat dry foods that did not meet NRC recommendations. After switching to a food that met the standards, the dermatosis fully resolved in all 13 (Sousa et al., JAVMA, 1988).

Foods like that have almost disappeared from the shelves, so the “food falls short of the standard” scenario has moved from the label into the bowl. These days it is more often the portion size that breaks the standard.

To see this, you need one number: how much protein a dog needs per day.

How much protein does a dog need for its hair to grow?

An adult 30 kg Labrador needs at least 63.5 g of protein, 4.6 g of linoleic acid and 25.4 mg of zinc a day (our own calculation from FEDIAF 2025).

In the FEDIAF tables the minimums are given per 1,000 kcal of food: 45 g of protein at an intake of 110 kcal/kg^0.75 and 52.1 g at 95. Both columns give the same absolute number, 4.95 g of protein per kg^0.75 per day.

FEDIAF warns separately that these are minimum recommended levels for commercial foods, not a dog's minimum requirement.

Then comes the arithmetic that breaks everything: the less a dog eats, the more protein each of its calories must carry.

Our own calculation: 4.95 g × 30^0.75 = 63.5 g of protein per day, divided by daily calories; kg^0.75 here means weight in kilograms to the power of 0.75. How the calorie amount itself is calculated is covered in the article on food amount by weight.

This is exactly where the most popular anti-shedding advice falls apart.

Will vitamins or biotin help with shedding?

A healthy dog on a complete food does not need added biotin, unless the food contains antimicrobial or antivitamin substances (FEDIAF 2025, section 3.3.1).

Let's test the advice on the Labrador. In winter his portion was cut to 897 kcal. A food with 20% protein and 373 kcal/100 g gives him 241 g of food and 48 g of protein on that portion, or 76% of the minimum. The same food on a normal 1,436 kcal portion gives 77 g of protein, 121%.

There was no vitamin shortage before or after. What was missing was protein, and it disappeared along with the portion.

Our own calculation from FEDIAF 2025. Energy of 373 kcal/100 g and protein of 26.3% were measured for 224 dry foods (Marchi et al., 2025); in the last column protein is per label and the energy of 397 kcal/100 g is calculated per NRC 2006, without lab confirmation.

With fat in the food, the story plays out differently, and the timelines are different too.

Will a higher-fat food change the coat?

Dietary fat mainly changes shine and softness: when fat was raised from 9 to 13%, shine and softness improved significantly in all dogs within 12 weeks, while the effect of fat type showed up only in week 12 (Kirby et al., 2009).

Seed supplements work for an even shorter time. In 18 healthy dogs, the numerical coat improvement after flaxseed or sunflower seed did not last longer than 28 days (Rees et al., Vet Dermatol, 2001).

Foods labeled “for skin and coat” have little in common: across 24 such foods, the content of skin-related nutrients varied widely (Johnson et al., 2015).

That leaves the question of when you can judge the result at all.

How long after a food change do you see results?

Coat density is assessed after 3–3.5 months: in 37 Labradors, a clipped patch returned to its previous length in 14.6 weeks in spring, 14.5 in summer, 13.6 in autumn and 15.4 in winter, and the difference between seasons was not statistically significant (Diaz et al., 2004). Shine and softness change faster, within a few weeks.

The typical mistake goes like this: the food is changed, no extra density shows after three weeks, the food is declared a failure and changed again. In three weeks the dog has not had time to grow a single full hair.

Nobody has managed to speed this up: in huskies, neither topical melatonin nor active brushing accelerated regrowth (Diaz et al., 2006).

How to switch a dog to a new food is covered in a separate article.

There are cases when you should not wait those three months.

When is food not the issue and it's time to see a vet?

See a vet if there is at least one of six signs: bald spots, patchy hair loss, symmetrical hair loss, itching, redness, flakes, or hair that does not grow back after clipping.

Such pictures are caused by hormonal and skin diseases, they are told apart by tests, and a food change will show nothing here.

If the dog is also scratching, the approach is different; it is covered in the article on a dog that keeps scratching.

If none of this applies, what remains is a three-month plan.

What to do if the hair is falling out right now?

• If there are no bald spots, itching or flakes, and the hair is simply coming out in spring or autumn, do not change the food: it is the season.
• If you cut the portion because of weight, check the protein per calorie: a 30 kg Labrador on 897 kcal needs 71 g of protein per 1,000 kcal instead of 44 g on a normal portion.
• To calculate for your own dog, get its calorie amount from the portion calculator and divide 4.95 g × weight^0.75 by it: the result is the protein needed per 1,000 kcal.
• If you have already changed the food, look at shine after three to four weeks and at density after 3–3.5 months, and do not change the food between those dates.
• For the Labrador from the start of the story, the plan is: 1,166 kcal a day, 63.5 g of protein, a food with at least 54 g of protein per 1,000 kcal, and a second look at density after 3.5 months.

He will still shed his coat in spring. The difference is that now the owners know why, and his bowl holds 82 g of protein instead of 48.

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