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: Systemic side effects including piloerection , headache , and cold extremities were experienced in all subjects .
### Output Text:
Systemic side effects including piloerection , headache , and cold extremities were experienced in all subjects . 