A dog losing hair on the sides may develop thinning fur, clearly defined bald patches, or broader areas where the skin becomes visible along the flanks or sides of the body.
The hair loss may occur on one side or both sides, and the exposed skin may look normal or become darker, scaly, red, crusty, or irritated.
The pattern can be especially helpful when hair loss occurs along both sides of the abdomen or flank area. Some dogs have itching and skin inflammation, while others develop relatively smooth, non-itchy hair loss.
Because these patterns can have different causes, a dog’s age, breed, progression of the hair loss, skin appearance, and other health changes all matter when determining what may be happening.
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Dog Losing Hair on Sides: What It Means
A dog losing hair on the sides may have seasonal flank alopecia, a hormonal disorder, allergies, parasites, infection, or another condition affecting the skin and hair follicles.
When hair loss occurs fairly evenly on both sides without itching, a hair-growth disorder or hormonal cause becomes more relevant.
When it is accompanied by intense itching, redness, crusting, or licking, an inflammatory or infectious skin problem is more likely.
The pattern of hair loss is an important diagnostic clue. Persistent or unexplained bald areas should be assessed by a veterinarian, especially when the skin changes color or texture or the dog develops other symptoms such as increased thirst, weight changes, or changes in energy.
Dog Losing Hair on Sides: Common Causes
Seasonal Flank Alopecia
Seasonal flank alopecia is one of the more distinctive causes of hair loss along a dog’s sides.
It typically produces sharply defined patches of hair loss on the flanks, often affecting both sides symmetrically. The exposed skin may become noticeably darker.
The condition tends to follow a seasonal pattern, with hair loss often beginning in one season and regrowth occurring several months later.
It can recur in subsequent years, and some dogs develop additional areas of hair loss along the sides of the chest, tail base, or other locations.
Seasonal flank alopecia is not usually associated with significant itching or inflammation.
However, other diseases can produce a similar pattern, so veterinarians may rule out hormonal disease, parasites, and fungal infection before making the diagnosis.
Related: Dog losing hair in patches and scabs (What it means)
Allergies
Allergies can cause itching that leads a dog to scratch, lick, or chew its skin. Repeated self-trauma can break hairs and eventually create visible areas of hair loss.
Allergic skin disease may affect the sides of the body along with the paws, ears, belly, groin, or face.
Redness, recurrent skin infections, scaling, or persistent itching can make an inflammatory skin problem more likely than a purely follicular hair-growth disorder.
Flea Allergy Dermatitis
Flea allergy dermatitis can cause intense itching and hair loss from repeated scratching and chewing.
Although the lower back and tail base are classic areas, affected dogs can develop irritation in other parts of the body.
If the sides are itchy and the dog is also chewing at the lower back, tail base, thighs, or abdomen, flea allergy may be considered. The absence of visible fleas does not by itself rule out flea exposure.
Related: Dog losing hair with blacks on the skin (Causes and what to do)
Mites and Other Parasites
Parasites such as mites can damage the skin and hair follicles, resulting in hair loss, scaling, redness, crusting, and itching.
Different mite infestations can produce different patterns, so the location of the bald areas alone cannot establish the cause.
Skin scrapings and other diagnostic tests may be used when parasites are suspected.
Bacterial Skin Infection
Bacterial skin infections can cause small or larger areas of hair loss, particularly when the infection involves the hair follicles.
Redness, scaling, crusting, bumps, or scabs may accompany the missing hair.
More superficial infections can produce multiple bald patches, while deeper infections may cause pain, swelling, odor, or discharge.
A bacterial infection may occur on its own or develop secondarily after allergies, parasites, or another condition damages the skin.
Yeast or Other Skin Infections
Yeast overgrowth can contribute to itchy, greasy, scaly, or discolored skin and may lead to hair loss through inflammation and repeated scratching.
When hair loss on the sides occurs with odor, greasy skin, redness, or recurrent skin problems, infection may need to be considered.
A veterinarian may examine skin samples to determine whether yeast or another infection is present.
Ringworm
Ringworm is a fungal infection that can cause localized hair loss, scaling, crusting, and broken hairs.
It can affect different parts of the body and sometimes produces clearly defined patches.
A dog does not need to have severe itching for ringworm to be present. Because the appearance can overlap with other causes of alopecia, fungal testing may be needed to confirm the diagnosis.
Hypothyroidism
Hypothyroidism can interfere with normal hair growth and produce relatively non-itchy hair thinning or hair loss.
The pattern can include the sides of the trunk, underside of the body, thighs, tail, and other areas.
Other possible signs include lethargy, weight gain, changes in the quality of the coat, and reduced hair regrowth.
Hypothyroidism is therefore more relevant when the hair loss occurs alongside broader changes in the dog’s health.
Related: Dog losing hair and itching (Here’s why)
Cushing Disease
Cushing disease, or hyperadrenocorticism, can cause hair loss and changes in the skin. Dogs may also develop increased thirst and urination, increased appetite, panting, weakness, a pot-bellied appearance, thin skin, or recurrent skin problems.
Hair loss on the sides alone does not mean a dog has Cushing disease. This possibility becomes more relevant when the coat changes are accompanied by several of these other signs.
Friction or Pressure
Repeated rubbing can cause localized hair loss on the sides of the body. This may occur where a harness, clothing, bedding, or another object repeatedly contacts the coat.
Friction is more likely when the hair loss corresponds closely to a particular contact area and the skin underneath is otherwise relatively normal.
However, persistent redness, itching, or inflammation suggests that another condition may be involved.
Excessive Licking, Scratching, or Chewing
Hair may be missing because the dog is repeatedly damaging it rather than because the follicles have stopped producing hair.
The underlying reason for this behavior could be an allergy, parasite, infection, pain, irritation, or another skin disorder.
Continued self-trauma can make the original problem harder to recognize because the skin becomes increasingly inflamed.
Follicular or Hereditary Hair Disorders
Some dogs develop inherited or follicular disorders that interfere with normal hair production. These conditions may cause symmetrical or patterned hair loss without significant itching or inflammation.
They are generally considered after more common causes such as parasites, infections, and allergies have been investigated.
A skin biopsy may be needed when the structure of the hair follicles needs to be examined.
Hair Loss After a Severe Illness
Temporary hair loss can occur after certain significant illnesses or episodes of fever. In these situations, the coat may enter an abnormal growth cycle and become noticeably thinner some time after the illness.
This type of hair loss is usually considered in the context of the dog’s recent medical history rather than from the side hair loss alone.
Related: Dog Losing Near Eyes (Causes and treatment)
Dog Losing Hair on Sides but Not Itching
A dog losing hair on the sides without itching may have a condition that affects the hair follicles or the hair-growth cycle rather than a problem caused by scratching.
Hormonal disorders such as hypothyroidism or Cushing’s disease can cause relatively symmetrical hair loss without significant itching.
Seasonal flank alopecia can also produce hair loss on the sides without obvious discomfort, particularly when it follows a recurring seasonal pattern.
If the skin is otherwise normal and the dog is not scratching, the cause may be less urgent than an itchy skin infection, but persistent or spreading hair loss should still be evaluated.
A veterinarian may examine the skin and consider blood tests or other testing if a hormonal disorder is suspected.
Dog Losing Hair on Both Sides
A dog losing hair on both sides may have symmetrical flank alopecia, hormonal disease, or another condition affecting the hair-growth cycle.
Hair loss caused by hormonal problems is often relatively symmetrical and may occur on the flanks, trunk, or other areas without intense itching.
Seasonal flank alopecia can also cause sharply defined hair loss on both sides of the body and may grow back later.
The timing, pattern, skin appearance, and whether the hair regrows are useful clues.
If the hair loss is accompanied by increased thirst, increased urination, changes in appetite, weight changes, lethargy, or a pot-bellied appearance, veterinary evaluation is particularly important.
Dog Losing Hair on One Side
A dog losing hair on one side may have a localized skin problem rather than a generalized hormonal or coat disorder.
Repeated licking or rubbing, an injury, infection, parasite infestation, allergy, or irritation from contact with a surface can cause hair loss in one area.
A dog may also lose hair on one side because of discomfort in an underlying joint or body area that causes repeated licking.
Look closely for redness, scaling, crusts, swelling, discharge, or broken hairs around the bald area. If the hair loss continues to expand, the skin changes, or the dog begins licking or scratching the area, a veterinarian should examine it to determine the cause.
Dog Losing Hair on Sides and Skin Turning Dark
A dog losing hair on the sides while the skin becomes darker may have chronic inflammation or a disorder affecting the hair-growth cycle.
Persistent licking and irritation can cause hyperpigmentation, in which previously lighter skin becomes darker.
Hormonal conditions, chronic allergies, recurrent skin infections, and some forms of flank alopecia can also produce hair loss accompanied by darker skin.
Darkening of the skin is usually a gradual change rather than an immediate sign of a specific disease.
If the skin is thickened, red, greasy, crusty, has an odor, or the hair loss continues to spread, veterinary examination is recommended because an underlying skin or hormonal condition may need treatment.
When to Call or Visit the Vet
Veterinary evaluation is appropriate when hair loss on the sides persists, spreads, or is accompanied by abnormal skin or other health changes.
Contact a veterinarian if your dog has:
Hair loss that is rapidly spreading or becoming extensive
Persistent scratching, licking, or chewing
Red, painful, swollen, or thickened skin
Scabs, crusts, sores, or discharge
Greasy skin or a strong odor
Significant or progressive darkening of the skin
Hair loss in several other areas
Recurrent skin infections
Increased thirst or urination
Increased appetite, panting, weakness, or a pot-bellied appearance
Noticeable weight or energy changes
Hair loss that repeatedly returns without an obvious explanation
Bald areas that do not begin to improve or continue to enlarge
Rapidly worsening skin changes, significant pain, open sores, or signs that the dog is generally unwell warrant more prompt veterinary assessment.
Dog Losing Hair on Sides: Treatment
Treatment depends on the underlying cause. The veterinarian may examine the distribution of the hair loss, the condition of the skin, and whether the hairs are being shed from the follicles or broken off.
Diagnostic testing may include flea and parasite evaluation, skin scrapings, cytology or cultures for infection, fungal testing, and blood tests when a hormonal or systemic disorder is suspected.
A skin biopsy may be recommended when the cause remains unclear or a follicular disorder such as seasonal flank alopecia needs confirmation.
Treatment is then directed at the specific diagnosis rather than the hair loss itself.
Key Takeaway
A dog losing hair on the sides can have an itchy skin problem such as allergies, parasites, or infection, but smooth, symmetrical, relatively non-itchy hair loss can point toward conditions that interfere with normal hair growth.
Seasonal flank alopecia is a particularly recognizable cause when sharply defined bald areas develop on both flanks and the exposed skin becomes darker.
Hormonal conditions such as hypothyroidism can also cause hair thinning along the sides, especially when other changes such as lethargy, weight gain, or coat abnormalities are present.
Because several conditions can look similar, persistent or unexplained hair loss is best evaluated based on the pattern, skin appearance, itching, progression, and the dog’s overall health.