Changes

===Type I reactions===

===Type I reactions===

*Mediated by pharmacologically active substances from [[Mast cells - Anatomy & Physiology|mast cells]] and [[Basophils - Anatomy & Physiology|basophils]]

*Mediated by pharmacologically active substances from [[Mast Cells - WikiBlood|mast cells]] and [[Basophils - WikiBlood|basophils]]

**Due to antigen-antibody (usually IgE) binding to receptors on those cells

**Due to antigen-antibody (usually IgE) binding to receptors on those cells

*Substances include histamine, serotonin, leukotriens, prostaglandins

*Substances include histamine, serotonin, leukotriens, prostaglandins

*Microscopically:

*Microscopically:

**Hyperplastic superficial perivascular dermatitis

**Hyperplastic superficial perivascular dermatitis

**Oedema, [[Mast cells - Anatomy & Physiology|mast cells]], [[Basophils - Anatomy & Physiology|basophils]], [[Eosinophils - Anatomy & Physiology|eosinophils]], [[Lymphocytes - Anatomy & Physiology|lymphocytes]], histiocytes

**Oedema, [[Mast Cells - WikiBlood|mast cells]], [[Basophils - WikiBlood|basophils]], [[Eosinophils - WikiBlood|eosinophils]], [[Lymphocytes - WikiBlood|lymphocytes]], histiocytes

**Fibropruritic nodules covered by hyperplastic epidermis

**Fibropruritic nodules covered by hyperplastic epidermis

**Mononuclear cells

**Mononuclear cells

**If chronic, epidermal hyperplasia

**If chronic, epidermal hyperplasia

**May involve [[Eosinophils - Anatomy & Physiology|eosinophils]]

**May involve [[Eosinophils - WikiBlood|eosinophils]]

==Autoimmune reactions==

==Autoimmune reactions==