Most types of dog skin disease look alike: redness, hair loss, crusts and spots appear in allergies, bacterial infections, yeast overgrowth, mites and ringworm. A picture can help you describe a lesion, but it cannot name the cause. Only tests such as cytology, skin scrapings or fungal culture can, so use the tables below to see which conditions fit what you can see, then use the decision guide to judge how soon your dog needs a vet.
This guide uses written descriptions rather than photographs, because the veterinary sources below say lesions cannot be reliably matched to a label by sight. For Australian owners it also covers one extra step: checking for paralysis ticks, because their early signs can be mistaken for a minor problem.
Check for ticks first if you live on the east coast
The University of Sydney’s veterinary hospital says the paralysis tick (Ixodes holocyclus) is a concern especially along the east coast, can be active through the year in Sydney with risk often higher in warmer months, and recommends daily tick checks around the head, ears, neck, under the collar, between the toes and under the tail (University of Sydney Vet Hospital, page modified June 2026). Early signs of tick paralysis include weakness or wobbliness, particularly in the hind legs, vomiting, coughing, gagging, or a change in bark or voice, and dogs with these signs or breathing difficulty need immediate veterinary attention.
A tick bite can also leave a local skin lesion, so a lump or scab on the head or neck is worth a careful look. That is a practical point, not a finding from the source above. If your dog is weak, wobbly or vomiting, do not wait to see whether a skin problem clears up.
How common are skin problems in dogs? (British data)
Very common, though we could not find equivalent Australian figures. The Royal Veterinary College’s VetCompass programme looked at 22,333 dogs in UK primary-care practice and found that 12.58 percent (95% CI 12.15 to 13.02) had a skin disorder recorded in the study year (O’Neill et al., BMC Veterinary Research 2021). These are British data, and rates may differ in Australia’s climate.
Why a photo cannot diagnose your dog’s skin disease
The Merck Veterinary Manual (professional version, May 2025) says “many skin diseases look alike” and that a definitive diagnosis comes from including or excluding possible causes and from watching the response to treatment. Its owner version adds that an immediate diagnosis may not be possible and that more than one visit is often needed (Merck, dog owners).
- Allergy. The international guideline on canine atopic dermatitis notes the “resemblance to other non-atopic related skin diseases” and recommends flea combing, skin scraping and cytology where needed (Hensel et al. 2015).
- Bacterial infection. The ISCAID guideline says cytology should be done in all pyoderma cases before antimicrobials are used (Loeffler et al. 2025).
- Ringworm. The World Association for Veterinary Dermatology consensus found no single diagnostic test to be the gold standard (Moriello et al. 2017).
- Lumps. Merck notes that mast cell tumours “can mimic lipomas” (Merck, tumors of the skin in dogs).
Software can recognise the type of lesion in an image, though not its cause. A 2026 study trained image models to flag erythema (redness), lichenification (thickened skin), alopecia (hair loss) and erosion or ulcer, with accuracy above 90 percent against veterinary labels (Kang et al., Veterinary Dermatology 2026). That describes what a lesion looks like, not which disease lies behind it.
We did not find a published study testing how often owners correctly name a skin disease by matching their dog to web photos. That is a gap in the evidence.
Types of dog skin disease: what they look like and where
These descriptions come from the Merck Veterinary Manual, Cornell University College of Veterinary Medicine and the studies named in each row. They show what is typical. Dogs vary, and several conditions often occur together because bacteria and yeast readily infect skin that is already inflamed.
| Condition | What it can look like | Where it often shows up | How a vet confirms it |
|---|---|---|---|
| Flea allergy dermatitis | Intense itch with small crusted spots and hair loss from chewing; long-standing cases can become hairless and darkened | Lower back, base of the tail and rear thighs (Merck) | History, fleas or flea dirt, and response to flea control |
| Environmental allergy (atopic dermatitis) and food allergy | Itching is the hallmark; scratching and licking cause redness, sores and often skin or ear infections. Food allergy itch shows little change between seasons | Paws, face, ears, front-leg creases, armpits and tummy; signs usually start between 6 months and 3 years (Merck) | Ruling out other causes. Merck states no test can positively identify atopy; food allergy needs a strict diet trial of up to 3 months because blood and skin tests are not reliable for it (Merck) |
| Hot spot (acute moist dermatitis) | A moist, inflamed, oozing patch that later forms a scab (Cornell) | In a study of 44 dogs, most often the cheek, neck and outer thigh (Holm et al. 2004) | Examination and cytology, plus a search for the trigger. An underlying cause was found or suspected in 31 of 44 dogs |
| Superficial bacterial pyoderma (folliculitis) | Pimple-like bumps or pustules around hair follicles, ring-shaped scales called epidermal collarettes, scabs and patchy hair loss. In short-coated dogs it can resemble hives, but the hairs pull out easily | Anywhere; warm, moist skin folds and pressure points are higher risk (Merck, professional; Merck, owners) | Cytology before any antimicrobial; the underlying cause (often allergy or parasites) must also be found |
| Deep pyoderma | Pain, crusting, odour, and bloody or pus-filled discharge, with possible swelling, ulcers and blisters | Bridge of the muzzle, chin, elbows, hocks, knees and between the toes | Veterinary examination; deep scrapings to exclude parasites, with bacterial or fungal cultures in some cases |
| Yeast (Malassezia) dermatitis | Red skin with greasy brown-black material matting the base of the hairs; darkening, thickening and odour are common, and itch is usually prominent | Skin folds and other moist areas (Guillot and Bond 2020) | Cytology, usually by tape strip. The yeast normally lives on skin, and overgrowth is most often tied to another disease |
| Sarcoptic mange (scabies) | Thick yellow crusts, scratch wounds, redness and hair loss | Tummy, chest, ears, elbows and hocks, spreading if untreated (Merck) | Skin scrapings; Merck notes scrapings can be negative, so a treatment trial may be warranted |
| Demodicosis (demodectic mange) | Localised form: one to five small, sharply bordered areas of hair loss, redness and scaling, with little or no itch. Generalised form: widespread lesions, often with infection | Localised form: around the lips and eyes and on the forelimbs | Deep skin scrapings are the diagnostic gold standard (Mueller et al. 2020) |
| Ringworm (dermatophytosis) | Bald, scaly patches with broken hairs; sometimes acne-like spots. People can catch it | Face, ear tips, tail and feet (Merck) | Fungal culture (called the most accurate), ultraviolet lamp and microscopy of hairs |
| Condition | What it can look like | Where it often shows up | How a vet confirms it |
|---|---|---|---|
| Skin tumours | Usually small lumps or bumps, but also hairless or discoloured patches, rashes or ulcers that do not heal | Anywhere on the body | Fine-needle aspiration or biopsy; Merck says identifying them should be left to a vet |
| Autoimmune skin disease | Pemphigus foliaceus: large, fragile pustules, then crusts and hair loss. Discoid lupus: pigment fading, redness, then erosions and ulcers | Pemphigus: ears and face, then feet. Discoid lupus: nose and footpads (Cornell) | Skin biopsy, after parasitic and drug-related causes are ruled out |
| Hives (urticaria) | Red, swollen, usually itchy patches that can appear and fade within hours (Merck) | Back, sides, neck, eyelids and legs | Veterinary assessment; the trigger (sting, medicine, vaccine, food or environment) is then sought |
Decision guide: how fast does this need a vet?
This sequence is our editorial synthesis of the sources cited, not a validated triage tool. If in doubt, phone your own practice and describe what you see.
- Emergency, go now. Hives or swelling together with sudden vomiting, heavy drooling, collapse or trouble breathing. Merck lists sudden diarrhoea, excessive drooling, vomiting and shock among anaphylaxis signs, calls a suspected reaction an emergency and advises seeking emergency veterinary help immediately (Merck, anaphylactic reactions). Hives after a vaccine or new medicine also warrant phoning your vet straight away. In Australia, a wobbly or weak dog, vomiting, coughing or gagging, or a changed bark should also be treated as an emergency until a tick has been ruled out.
- Same day. Painful lesions, pus, blood, discharge or a strong odour (signs of deep infection); a hot spot more than 24 hours old or showing spreading redness, heat or swelling (Cornell); or a dog that also seems unwell. Merck notes the skin can be the first place body-wide illness shows.
- Within a few days. A skin problem that has not cleared in a few days, any bald scaly patch (ringworm can pass to people and other animals), recurring itch, or any new lump.
- While you wait. Do a full tick search, then check for fleas with a flea comb, since flea dirt is a recognised clue (Merck). Stop your dog chewing the area if you can do so safely, and ask the practice whether to hold off on shampoos or creams before the appointment, because they may complicate the examination. If itching is the main worry, our guide to why dogs itch so much explains the common causes.
How to take photos your vet can use
Photos are valuable as a record. These steps are practical suggestions, not findings from a study.
- Take one close-up and one wider shot showing where on the body the lesion sits, in daylight, with a coin or ruler beside it for scale.
- Repeat the same shots every day or two. A lesion that is spreading, deepening or oozing more tells your vet something a single photo cannot.
- Write down when it started, how much your dog scratches or licks, whether it comes and goes with the seasons, and any new food, medicine or flea product. Merck stresses that diagnosis starts with a detailed history.
- Keep any fleas, flea dirt or ticks you find.
Common misreadings of skin photos
| Assumption | What the sources say |
|---|---|
| “If it matches the picture, I know what it is.” | Many skin diseases look alike, and diagnosis often needs tests and several visits (Merck). |
| “A round bald patch is ringworm.” | Ringworm is confirmed by culture, ultraviolet lamp and microscopy,. Shape alone does not settle it. |
| “No mites on a scraping means no mange.” | Merck notes that a definitive diagnosis of sarcoptic mange is sometimes difficult because scrapings are negative; a treatment trial may be justified. |
| “Dark, greasy, smelly skin is just yeast.” | Yeast overgrowth is usually secondary to another disease, and diagnosis is by cytology (Guillot and Bond). |
| “A lump that looks harmless is harmless.” | Mast cell tumours can mimic lipomas (Merck). A needle sample or biopsy is how vets tell. |
What we know and what remains uncertain
- Well supported: that cytology, scraping, culture and biopsy are standard tools, and that many skin diseases look alike (veterinary guidelines and the Merck Veterinary Manual).
- Expert guidance rather than trial evidence: the appearance descriptions and sites in the tables. Individual dogs vary by breed, coat and stage of disease.
- Limited data: the hot spot figures come from a single study of 44 dogs in Sweden, in an area without endemic fleas, so they may not apply everywhere.
- Not found: a study measuring how accurately owners identify skin disease from photographs.
Frequently asked questions
What are the most common types of dog skin disease?
Allergies (including flea allergy), bacterial skin infections, yeast overgrowth, mites, hot spots and ringworm are among the most frequently discussed. In a large British VetCompass study, 12.58 percent of dogs had a skin disorder recorded in the study year; we did not find an Australian equivalent.
Can I diagnose my dog’s skin problem from a picture?
No. Many conditions look alike, and veterinary guidelines rely on cytology, skin scrapings, fungal culture, diet trials or biopsy to find the cause. Photos are best used to record how a lesion changes.
What does a bacterial skin infection look like on a dog?
Typically pimple-like bumps or pustules around hair follicles, crusts, scales, patchy hair loss and ring-shaped scales called epidermal collarettes. Deep infections are painful and may discharge pus or blood.
Could a skin problem on my dog actually be a tick?
Sometimes a tick is attached under the skin, and tick paralysis can begin with weakness, wobbly hind legs, vomiting, coughing or a changed bark. The University of Sydney Vet Hospital recommends daily tick checks and says affected dogs need immediate veterinary attention.
Which dog skin problems are contagious?
Sarcoptic mange spreads easily between dogs by contact and can affect people (Merck, dog owners). Ringworm also passes from animals to people through contact with infected animals or objects such as grooming tools. Ask your vet whether other pets or family members need attention.
When is a dog skin problem an emergency?
Hives or swelling with vomiting, heavy drooling, collapse or trouble breathing needs emergency veterinary care immediately. Painful, pus-filled or rapidly worsening lesions need a same-day appointment.
Should I put cream or shampoo on a skin problem before the vet appointment?
Ask your practice first. The right product depends on the cause, which is not known until a vet examines the skin, and the ISCAID guideline recommends cytology before any antimicrobial is used.
This article is educational and does not replace an examination by a veterinarian. Contact your vet about any skin change that persists, spreads, hurts or comes with other signs of illness.
Sources
- Merck Veterinary Manual, Moriello KA. Diagnosis of Skin Diseases in Small Animals (professional). 2025-05. merckvetmanual.com
- Merck Veterinary Manual, Moriello KA. Diagnosis of Skin Disorders in Dogs (owners). 2024-09. merckvetmanual.com
- Merck Veterinary Manual, Clark MD. Pyoderma in Dogs and Cats. 2025-10. merckvetmanual.com
- Merck Veterinary Manual, Moriello KA. Pyoderma in Dogs (owners). 2024-09. merckvetmanual.com
- Merck Veterinary Manual, Dryden MW. Mange in Dogs and Cats. 2025-05. merckvetmanual.com
- Merck Veterinary Manual, Dryden MW. Mite Infestation (Mange, Acariasis, Scabies) in Dogs (owners). 2026-04. merckvetmanual.com
- Merck Veterinary Manual, Gentry C. Flea Allergy Dermatitis in Dogs and Cats. 2026-05. merckvetmanual.com
- Merck Veterinary Manual, Hoff S. Atopic Dermatitis in Dogs. 2026-05. merckvetmanual.com
- Merck Veterinary Manual, White SD, Moriello KA. Allergies in Dogs (owners). 2024-09. merckvetmanual.com
- Merck Veterinary Manual, Merchant SR. Ringworm (Dermatophytosis) in Dogs (owners). 2026-06. merckvetmanual.com
- Merck Veterinary Manual, Villalobos AE. Tumors of the Skin in Dogs (owners). 2026-04. merckvetmanual.com
- Merck Veterinary Manual, White SD. Hives and Rashes (Urticaria) in Dogs (owners). 2024-09. merckvetmanual.com
- Merck Veterinary Manual, Tizard IR. Disorders Involving Anaphylactic Reactions in Dogs (owners). 2026-06. merckvetmanual.com
- Hensel P, Santoro D, Favrot C, Hill P, et al. Canine atopic dermatitis: detailed guidelines for diagnosis and allergen identification. BMC Vet Res. 2015;11:196. PMID 26260508. DOI 10.1186/s12917-015-0515-5. bmcvetres.biomedcentral.com
- Loeffler A, Cain CL, Ferrer L, Nishifuji K, et al. Antimicrobial use guidelines for canine pyoderma by ISCAID. Vet Dermatol. 2025;36(3):234-282. PMID 40338805. DOI 10.1111/vde.13342. pubmed.ncbi.nlm.nih.gov
- Moriello KA, Coyner K, Paterson S, Mignon B. Diagnosis and treatment of dermatophytosis in dogs and cats: WAVD Clinical Consensus Guidelines. Vet Dermatol. 2017;28(3):266-e68. PMID 28516493. DOI 10.1111/vde.12440. pubmed.ncbi.nlm.nih.gov
- Mueller RS, Rosenkrantz W, Bensignor E, et al. Diagnosis and treatment of demodicosis in dogs and cats: WAVD Clinical Consensus Guidelines. Vet Dermatol. 2020;31(1):5-27. PMID 31957202. DOI 10.1111/vde.12806. pubmed.ncbi.nlm.nih.gov
- Guillot J, Bond R. Malassezia yeasts in veterinary dermatology: an updated overview. Front Cell Infect Microbiol. 2020;10:79. PMID 32181160. DOI 10.3389/fcimb.2020.00079. frontiersin.org
- Holm BR, Rest JR, Seewald W. A prospective study of the clinical findings, treatment and histopathology of 44 cases of pyotraumatic dermatitis. Vet Dermatol. 2004;15(6):369-76. PMID 15585012. DOI 10.1111/j.1365-3164.2004.00421.x. pubmed.ncbi.nlm.nih.gov
- Kang et al. Artificial intelligence-based identification of common canine skin lesions from clinical images. Vet Dermatol. 2026. PMID 42067986. DOI 10.1111/vde.70083. pubmed.ncbi.nlm.nih.gov
- O’Neill DG, James H, Brodbelt DC, Church DB, Pegram C. Prevalence of commonly diagnosed disorders in UK dogs under primary veterinary care. BMC Vet Res. 2021;17:69. PMID 33593363. DOI 10.1186/s12917-021-02775-3. bmcvetres.biomedcentral.com
- Cornell University College of Veterinary Medicine, Riney Canine Health Center. Hot spots (DogWatch reprint, no date shown). vet.cornell.edu
- Cornell University College of Veterinary Medicine, Riney Canine Health Center. Canine skin autoimmune diseases (DogWatch reprint, no date shown). vet.cornell.edu
- University of Sydney Veterinary Hospital. Ticks (paralysis tick, Ixodes holocyclus). Page modified 2026-06-26. sydney.edu.au
Dogs Australia, RSPCA Australia and the Australian Veterinary Association publish owner-facing information. We have not cited them because we did not verify a skin-specific page from any of them.