In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Stevens - Johnson syndrome is a well - recognized immune complex - mediated hypersensitivity reaction that affects all age groups , is drug or infection induced , and has classic systemic , mucosal , and dermatologic manifestations .
### Output Text:
Stevens - Johnson syndrome is a well - recognized immune complex - mediated hypersensitivity reaction that affects all age groups , is drug or infection induced , and has classic systemic , mucosal , and dermatologic manifestations . 