comparison of irritant and allergic dermatitis
Last reviewed 01/2018
| primary irritant | allergic contact | |
| Prior exposure | none required | sensitisation needed to substance |
| Spread | little extension from contact site | may spread to sites not in direct contact |
| Association | atopy predisposes | prolonged use of topical medicaments may predispose |
| Susceptibility | everyone | only certain people |
| Course | Rapid onset within 4-12 hours. Lesions develop on first exposure | Onset usually after 24 hours. No lesions on first exposure. |