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: However , it is not known that how pain intensity ratings are affected by attention in capsaicin - induced secondary hyperalgesia .
### Output Text:
However , it is not known that how pain intensity ratings are affected by attention in <span class="chemical">capsaicin</span> - induced secondary hyperalgesia . 