SYMPTOM
Skin thinning or bruising
Skin that appears fragile, tears more easily, or shows bruising without obvious external trauma.
Endocrine (Hyperadrenocorticism)
Excess cortisol production is one of the most well-recognised causes of skin thinning and easy bruising in dogs. Chronically elevated cortisol levels affect the skin's collagen structure, reducing its thickness and elasticity while also weakening blood vessel walls. The skin may become visibly thinner, sometimes to the point where underlying blood vessels are visible through the surface, and bruises may appear after handling that would not normally cause injury. These changes typically develop alongside other signs of cortisol excess such as increased thirst, a pot-bellied appearance, and coat changes.
Coagulation Disorders
Abnormalities in the blood's clotting mechanisms can produce easy bruising even with normal skin thickness. Conditions affecting platelet numbers or function, clotting factor deficiencies, and diseases that consume clotting components can all result in bruising that appears disproportionate to the level of trauma involved. The bruising pattern may include petechiae, ecchymoses, or both, and may affect skin, mucous membranes, and other tissues.
Medication Effects
Certain medications, particularly long-term corticosteroids and some other immunosuppressive drugs, can produce skin thinning and increased bruising susceptibility as side effects. Corticosteroids mimic the effects of endogenous cortisol on skin structure, and prolonged use can produce changes similar to those seen in naturally occurring hyperadrenocorticism. These iatrogenic skin changes may develop gradually during treatment and can vary depending on dose and duration.
Hepatic
The liver produces many of the proteins involved in blood clotting, and significant liver dysfunction can impair the production of clotting factors, leading to increased bruising tendency. Additionally, liver disease can affect the metabolism of hormones and other substances that influence skin integrity. Animals with advanced liver disease may show bruising alongside other signs of hepatic compromise such as jaundice, fluid accumulation, and changes in appetite.
Immune-Mediated
Immune-mediated conditions can target platelets or other components of the clotting system, producing bruising through immune-mediated destruction of these essential blood components. Immune-mediated thrombocytopenia, where the body's immune system attacks its own platelets, is a relatively well-recognised cause of spontaneous bruising in dogs. The bruising may appear suddenly and can affect multiple body areas, sometimes producing dramatic discolouration.
Why timing matters
Early observation
Early skin thinning may be difficult to detect, manifesting as a subtle change in skin texture or an increased tendency for minor scratches or abrasions to occur during normal handling. The skin may feel papery or fragile compared with its previous texture, and small bruises may appear in areas subject to everyday contact. These early changes can develop over weeks to months and may initially be attributed to ageing or normal variation.
Later presentation
As skin thinning progresses, the changes become more visually apparent. The skin may appear translucent, with blood vessels clearly visible beneath the surface, particularly over the abdomen and inner thighs. Bruising may occur with minimal provocation, and the skin may tear easily during handling, grooming, or blood sampling. Hair loss over affected areas may further expose the altered skin, creating a distinctive appearance.
The rate at which skin thinning and bruising develop depends on the underlying cause. Endocrine-driven changes typically progress gradually over months, while medication-related effects may develop more predictably in relation to treatment duration and dose. Coagulation disorders may produce bruising that develops acutely. Immune-mediated conditions may cause rapid-onset bruising over hours to days. Tracking the locations, size, and frequency of bruises provides a record that can help characterise the underlying process.
Conditions commonly associated
When to explore further
Bruising that appears without identifiable trauma, or that seems disproportionate to the level of handling or activity involved, may suggest that the skin or clotting system is compromised. Spontaneous bruising — where discolouration appears without any recalled injury — is particularly noteworthy.
Skin thinning that develops alongside other systemic changes such as increased thirst and urination, abdominal distension, muscle wasting, or coat changes may suggest an endocrine process affecting multiple body systems simultaneously. The combination of skin changes with these additional signs can be more informative than the skin changes alone.
Easy bleeding from minor wounds, prolonged bleeding from cuts, or blood in the urine or stool occurring alongside bruising may suggest a more generalised problem with blood clotting rather than skin thinning alone. These additional bleeding signs can provide important context about the nature of the underlying disorder.
Bruising that develops acutely — multiple bruises appearing over hours to days in a previously unaffected animal — may suggest an acute-onset clotting disorder that differs from the gradual progression of endocrine or medication-related skin changes. The speed of onset can help distinguish between different categories of causes.
Skin changes that develop during or shortly after starting a new medication, particularly corticosteroids or other immunosuppressive drugs, may represent a medication-related effect. The temporal relationship between medication introduction and the development of skin changes can be informative.
Photographing areas of bruising or skin thinning with a size reference provides documentation that can be compared over time and shared with veterinary professionals. Noting the location, size, and any recalled precipitating cause for each new bruise helps build a record that may reveal patterns. Observing the gum colour and looking for pinpoint reddish spots on the gums, inner ear flaps, or belly can provide additional information about whether the bruising tendency extends to other tissues. Handling the animal gently and avoiding rough grooming or play that might cause skin tears helps reduce the risk of injury while the underlying cause is being explored.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS