Cutaneous vasculitis can have various causes including but not limited to medications, bacterial and viral infections or allergens. It is estimated that 45–55% of cases are idiopathic, meaning the cause is unknown. In cases where a cause can be determined, medications and infectious pathogens are most common in adults, while IgA vasculitis (Henoch–Schönlein purpura) frequently affects children. Other etiologies include autoimmune conditions and malignancies, usually hematologic (related to the blood). +Most Common Etiologies in Adults Cause Frequency Examples Idiopathic 45–55% Cause unknown Infection 15–20% Staphylococcus and Streptococcus spp. Autoimmune 15–20% Rheumatoid arthritis, Systemic lupus erythematosus Medications 10–15% Antibiotics, nonsteroidal anti-inflammatory drugs (NSAIDs) The<unk><unk> s in the skin affected are located in the superficial dermis and include arterioles<unk>  arteries carrying blood to capillaries), capillaries, and venules<unk>  veins receiving blood from capillaries). In general, immune complexes deposit in<unk>  walls leading to activation of the complement system. C3a and C5a, proteins produced from the complement system, attract neutrophils to the<unk> s. Once activated, neutrophils then release preformed substances, including enzymes causing damage to<unk>  tissue. Evidence of this process can be seen with a sample of removed skin tissue, or biopsy, viewed under a microscope. Neutrophils are seen surrounding blood<unk> s and their debris within<unk>  walls, causing fibrinoid necrosis. This finding on histological examination is termed "leukocytoclastic vasculitis". Considering the wide range of potential causes leading to<unk> , there are subtle variations in the underlying pathophysiology for each cause. For example, medications are metabolized to<unk> er molecules that can attach to proteins in the blood or<unk>  walls. The immune system senses these altered proteins as foreign and produces antibodies in efforts to eliminate them from the body. A similar process occurs with infectious agents, such as bacteria, in which antibodies target microbial components.
Cutaneous small-vessel vasculitis
Livedoid vasculitis
Urticarial vasculitis
Systemic vasculitis
Acute cutaneous lupus erythematosus
Bullous small vessel vasculitis
Subacute cutaneous lupus erythematosus
Poikiloderma vasculare atrophicans