The main important conditions to be distinguished in a patient presenting with a rash and/or itching
| Rash+/−itch | Itching alone |
|---|---|
| Immune system mediated | Immune system mediated |
| Anaphylaxis | Anaphylaxis |
| Anaphylactoid reaction | Anaphylactoid reaction |
| Allergic reaction—local | Systemic |
| Urticaria (“hives”) and/or angioedema Idiopathic thrombocytopaenic | Systemic upset (for example, uraemia, cholestasis, blood disorders) |
| purpura (ITP) | Other |
| Infective | Senile itch |
| Bacterial | Solid tumours |
| Meningococcal septicaemia | HIV |
| Cellulitis | |
| Impetigo | |
| Scarlet fever | |
| Viral | |
| Varicella zoster | |
| Primary infection (chickenpox) | |
| Reactivation (herpes zoster or “shingles”) | |
| Measles | |
| Rubella (German measles) | |
| Non-specific viral rash | |
| Other conditions | |
| Henoch Schonlein purpura | |
| Psoriasis | |
| Eczema |