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: We suspect that the potential for caffeine to stabilize high resistance states in susceptible persons suggests that its use may facilitate their disease progression , as well as hinder accurate diagnosis and treatment .
### Output Text:
We suspect that the potential for <span class="chemical">caffeine</span> to stabilize high resistance states in susceptible persons suggests that its use may facilitate their disease progression , as well as hinder accurate diagnosis and treatment . 