Hot spots in dogs: acute moist dermatitis

Overview

A hot spot is a type of surface skin infection called surface pyoderma. Surface infection is confined to the outermost horny layer of skin. Here, the word pyotraumatic means inflammation associated with self-inflicted skin damage.

Lesions develop particularly on the back, tail base, side of the thigh, neck and face. A large, painful area can develop within hours on previously normal-looking skin. An ordinary surface hot spot usually heals well and is not itself life-threatening. However, deep hair follicle inflammation may lie beneath a similar-looking lesion.

Surface pyoderma is distinguished from superficial pyoderma, which extends into the epidermis and may involve hair follicles. Deep pyoderma reaches the dermis. These similar names therefore describe different depths of inflammation.

Causes

Initially, the skin itches or develops a small injury. Your dog starts working at the area with tongue, teeth or claws. Moisture trapped beneath hair provides a place for bacteria to grow. Inflamed skin leaks more fluid, encouraging bacterial multiplication. This creates a self-perpetuating cycle of itching and skin damage.

Common starting causes include allergies and external parasites such as fleas. An ear infection can make a dog scratch the skin beneath the ear raw. Anal gland inflammation or blockage can trigger licking around the tail. Sometimes the irritant is plant material or another foreign substance caught in the coat.

Staphylococcal bacteria normally live on healthy dogs' skin too. Damage to the skin barrier allows bacterial infection to develop. Finding a bacterium therefore does not explain the whole cause: the same bacterium may belong to the normal skin microbiota. Licking irritates superficial nerve endings and increases itching further.

Risk factors

A long, thick coat predisposes to hot spots. Newfoundlands, German Shepherd Dogs and Golden Retrievers are examples of susceptible breeds. Drooping ears also increase risk. Hot spots can occur in any season, although cases are more frequent in warm weather. Swimming, paddling or summer rain increases risk if a dense coat does not dry properly.

Mats hold water near the skin and prevent air reaching it. Joint or back problems may increase licking over a painful area. A dog lying on the same side for a long time may develop abrasions over bony prominences. Repeated licking associated with lack of activity can also start a lesion.

Reduced muscle mass in an older dog may leave less protective padding over bony prominences. An underlying allergy may involve food or environmental allergens encountered through the airways.

Typical symptoms

You may first notice your dog's constant interest in one spot. Intense scratching or biting can be the first visible sign. Long hair can hide the skin change. Gently parting the hair may reveal wet, red skin. Typical local changes include:

• Clear redness in the inflamed area.
• A wet, oozing surface with pus-like fluid sticking to the hair roots.
• An unpleasant smell.
• Pain or avoidance of touch.
• Hair loss over the lesion.
• A crust over the moist skin change.

A lesion beneath an ear can be associated with an ear infection. A site beneath the tail may go unnoticed because of the coat.

Local swelling may also be present. Inflammation makes the area warm, which gives the condition its name. Hair stuck to wet discharge can hide the lesion's true extent before examination.

Complications and consequences

Continued licking and biting enlarge the lesion and delay healing. Surface skin inflammation can also be accompanied by deeper infection. Deep infection may cause nodules and tracts draining through the skin. Severe deep inflammation can be associated with enlargement of local lymph nodes. Treatment of these findings differs from treatment of an ordinary surface lesion.

Recurrence is common if the original cause remains unidentified or cannot be controlled. The outlook for treated surface inflammation is usually good. The surface briefly drying does not correct an ongoing allergic itch, for example.

Diagnosis at the vet

The vet asks when signs began and performs a general examination to look for underlying causes. Inspecting the skin and coat shows the location and extent of the change. Hair may need clipping around it so the inflamed area's edges are visible. The edges are checked particularly for bumps, pustules and swelling compatible with deep infection.

Skin cytology, or examination of a cell sample, helps confirm the role of bacteria. A sample can be collected with adhesive tape, for example. Malassezia yeast is also considered. An ordinary surface infection treated topically does not usually need bacterial culture. Culture may be needed for deep, recurring or suspected resistant infection.

Recurring signs may require parasite samples or an elimination diet investigating food allergy. Ears and anal glands are examined as possible sources of itching or pain. An unusual or poorly healing change may need a biopsy to investigate other diseases.

Cytology can be examined at the practice, providing an immediate result. Bacteria found inside inflammatory cells support a bacterial infection diagnosis. Samples can also distinguish non-bacterial inflammatory diseases from similar-looking bacterial lesions. Culture results are interpreted alongside skin findings and cytology, as bacteria can grow even from healthy skin.

When investigating parasites, material brushed from the coat can be examined microscopically for fleas or Cheyletiella mites. Skin scrapings can look for sarcoptic or Demodex mites. If the underlying cause remains unclear, blood and urine tests may help identify another illness.

Distinguishing a hot spot from deep pyotraumatic folliculitis is not always easy by appearance. The distinction was difficult even from tissue samples in a study of 44 dogs.

Treatment

The vet prescribes medication based on skin findings and the underlying cause. The first aim is to stop continuous self-inflicted damage. A collar prevents your dog from reaching the area to lick or bite it. Hair is clipped from the inflamed area and around it. Clipping extends at least 2–3 cm beyond the visible skin lesion. Handling painful skin may require sedation.

Discharge and dirt are removed so topical treatment can reach the skin. Topical antiseptic treatment is the first-choice approach for surface infection. Antiseptics are preferred to topical antibiotics. An ordinary hot spot does not require oral antibiotics. Clipping hair and applying a topical antiseptic are treatment principles for a local surface infection.

Your dog may also need vet-prescribed medicines to reduce itching and inflammation. Pain relief makes local care of painful skin easier. Redness, oozing and pain should decrease within the first 48 hours after treatment begins. Crusting and skin recovery often take another 7–10 days.

Clinical and cytological resolution of surface pyoderma can usually be expected within 7–14 days. If progress is poor, the vet reassesses the skin and cytology. How treatment has been carried out and investigation of the original cause are reviewed at the same time. Any underlying ear infection is also treated.

Treating the underlying cause is different from topical care of the moist skin patch. A blocked anal gland may need emptying. Osteoarthritis pain can be treated with vet-prescribed pain relief. Depending on the circumstances, allergy is managed through allergen avoidance or immunotherapy. Food allergy may require a specifically selected diet. Training and environmental enrichment can be used for behaviour-related licking.

Prevention

Prevention targets both coat condition and causes of itching. External parasite control reduces parasite-related skin irritation. Groom a long or thick coat regularly and remove trapped plant material. Deal with mats because they retain moisture near the skin. After swimming, rinse your dog with clean water and dry thoroughly.

A long or double coat may need brushing and blow-drying as well as a towel to dry properly. Managing allergic skin disease is part of preventing recurrence. Monitoring ear redness, moisture and discharge helps identify an irritation source. In repeated cases, control of the underlying cause is essential even if the skin patch itself heals quickly.

Coat-care needs may change with the season, and some dogs benefit from seasonal trimming. Removing plant material prevents both matting and direct penetration into the skin.

Important for dog owners

Record when you noticed licking and how large the area looked initially. Take a photograph showing the lesion's location too. Tell the vet about swimming, ear signs, itching and previous similar lesions. This preserves the sequence of events. Check whether the protective device really prevents access to the skin: unnoticed licking or rubbing may explain poor treatment response.

Do not cut hair over an inflamed area with scissors at home, as the skin can be badly injured. Pain may make your dog defend themselves against handling. Do not remove a healthy scab, as this can delay healing. If redness persists after 48 hours of treatment or the lesion spreads, contact the vet treating your dog again.

Also stop another pet licking the sore area before your appointment. Avoid touching a fresh lesion with bare fingers, as contact may hurt and transfer bacteria. With repeated or severe signs, examination by a vet experienced in skin disease may help identify the trigger.

Frequently asked questions

Does a hot spot always need antibiotics?

An ordinary surface hot spot is treated primarily with topical care, avoiding oral antibiotics. The vet first checks that infection is not deep. Bumps, pustules and swelling at the edges can indicate deep infection requiring different treatment.

How quickly should the skin heal?

Redness and oozing should decrease within the first 48 hours after treatment starts. Skin recovery takes longer than the initial improvement. Surface pyoderma can usually be expected to resolve within 7–14 days, and a poorly progressing lesion is re-examined.

Can swimming cause a hot spot?

Swimming increases risk if a thick coat stays damp and does not dry properly. Moisture is trapped particularly beneath mats. Thorough drying and detangling are therefore useful preventive measures, especially for a dense-coated dog that swims frequently in warm weather.

Why does my dog keep getting hot spots?

Recurrence may indicate that the original cause of itching or pain continues. Allergy can sustain itchy skin. Anal gland inflammation can make a dog lick and bite the skin repeatedly. Treating each new patch alone does not remove the underlying cause of recurrence.

Can I treat the area with a human cream?

Do not choose a human medicine for your dog yourself. Some human medicines are poisonous to dogs. The vet treating your dog chooses a suitable skin product. Hair removal and skin cleaning are central treatment steps before applying a topical product.