A hotspot on a dog’s skin is caused by self-inflicted trauma: the dog scratches, licks, or chews one area so intensely that the skin breaks down, creating a raw, oozing sore that can spread within hours. The underlying trigger is almost always something that made the skin itchy or painful in the first place, such as allergies, fleas, or trapped moisture in a thick coat. Once the dog starts damaging the area, bacteria that normally live harmlessly on the skin multiply rapidly in the warm, moist wound, making the irritation worse and fueling a vicious cycle of scratching and spreading.
The medical name is acute moist dermatitis, and understanding the specific cause behind your dog’s hotspot is the key to stopping it from coming back.
How a Hotspot Forms
Every hotspot starts with something that bothers the skin enough to make a dog chew or scratch at it. That initial irritation could be a flea bite, an allergic reaction, a small scrape, or even moisture trapped against the skin after a swim. The dog’s response, repeated licking and scratching, strips away the protective outer layer of skin and creates a warm, wet environment that bacteria love.
Bacteria that are a normal part of a dog’s skin flora then overgrow on the damaged surface. In most cases this stays at the surface level rather than becoming a true deep infection, but without treatment, the bacterial overgrowth can push deeper into hair follicles and surrounding tissue. The combination of bacterial irritation and the dog’s continued self-trauma is what makes hotspots expand so quickly. A patch that was barely noticeable in the morning can be a palm-sized raw lesion by evening.
The Most Common Triggers
Allergies and external parasites, especially fleas, are the primary causes. A single flea bite can set off an intense allergic reaction in sensitive dogs, and the resulting scratching spirals into a hotspot before you even spot the flea. Environmental allergies to pollen, grass, or mold work the same way: widespread itchiness leads the dog to fixate on one spot.
Ear infections are another frequent culprit, particularly when wet ears from swimming or bathing aren’t dried properly. The dog scratches at the painful ear, and a hotspot develops on the skin just below or behind it. Anal gland problems trigger a similar pattern: discomfort near the tail drives licking and chewing that damages the skin over the hip or rear end.
Moisture is a major contributor on its own. A dog that goes swimming, walks through wet grass, or gets caught in a summer rain can develop a hotspot if the coat doesn’t dry completely. Water trapped against the skin softens it and creates ideal conditions for bacterial overgrowth. Matted fur makes this worse by holding moisture in place and blocking airflow.
Why Some Dogs Get Hotspots More Than Others
Dogs with heavy, dense undercoats are significantly more susceptible. Breeds like Golden Retrievers, Labrador Retrievers, German Shepherds, and Saint Bernards have thick double coats that trap heat and moisture against the skin, dry slowly, and provide poor ventilation. This creates the warm, damp microenvironment that bacteria thrive in. Warm weather compounds the problem, which is why hotspot cases spike in summer, though they can occur any time of year.
Dogs with underlying allergies, whether to food, fleas, or environmental triggers, are also repeat offenders. If the root cause of the itching isn’t addressed, new hotspots tend to appear in the same areas or pop up in different locations throughout allergy season.
The Role of Bacteria
A common misconception is that hotspots are bacterial infections that land on the skin from the outside. In reality, the bacteria involved already live on your dog’s skin as part of its normal microbiome. The most common species is one that colonizes the skin and mucous membranes of virtually all dogs. Under normal conditions it causes no harm, but when the skin barrier is broken and the surface stays moist, these bacteria multiply rapidly on the exposed tissue.
Most hotspots involve surface-level bacterial overgrowth rather than a deep infection. That’s an important distinction because it means the primary problem is the skin damage and moisture, not an invading pathogen. However, if a hotspot goes untreated, bacteria can push into hair follicles and deeper skin layers, turning a surface issue into a more serious infection that’s harder to resolve.
What Makes Hotspots Spread So Fast
The speed of hotspot development catches many dog owners off guard. The feedback loop is straightforward but relentless: irritation causes scratching, scratching damages skin, damaged skin allows bacterial overgrowth, bacterial overgrowth increases irritation, and the dog scratches harder. Each pass through this cycle expands the affected area. The warmth and moisture from oozing fluid and saliva from licking keep the wound from drying out or scabbing over, which would normally slow the process down.
This is why early intervention matters so much. Breaking the cycle at any point, whether by removing the initial trigger, stopping the dog from reaching the area, or drying out the wound, can halt the rapid spread.
Other Meanings of “Hotspot”
The term “hotspot” appears in several other fields, and you may have landed here looking for one of these instead.
Volcanic Hotspots
In geology, a hotspot is an area where unusually hot material rises from deep in the Earth’s interior, melting through the tectonic plate above it and producing volcanic activity. The Hawaiian Islands are the classic example: the Pacific Plate slowly drifts over a stationary plume of heat in the mantle, and each island formed as the plate carried the previous volcano away from the magma source and a new one built up in its place. This theory, proposed by geophysicist J. Tuzo Wilson in 1963, explains why volcanic island chains form in long, linear sequences. More recent research has questioned whether these plumes are truly stationary or as deep as originally assumed, but the basic framework remains widely used.
Urban Heat Islands
Cities create temperature hotspots because pavement, rooftops, and buildings absorb and re-emit far more solar energy than natural landscapes do. Trees and vegetation cool the air through shade and by releasing water vapor from their leaves, and natural water bodies add further cooling through evaporation. Urban areas replace these surfaces with dark, hard materials that reflect less sunlight and retain more heat, which is why a city center can be several degrees warmer than surrounding rural areas on the same day.
Biodiversity Hotspots
In conservation biology, a biodiversity hotspot is a region that meets two strict criteria: it contains at least 1,500 plant species found nowhere else on Earth, and it has already lost at least 70 percent of its original native vegetation. These areas are conservation priorities because they hold irreplaceable species diversity in a shrinking habitat. There are currently 36 recognized biodiversity hotspots worldwide.