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: BACKGROUND : Tacrolimus ointment is increasingly used for anti - inflammatory treatment of sensitive areas such as the face , and recent observations indicate that the treatment is effective in steroid - aggravated rosacea and perioral dermatitis .
### Output Text:
BACKGROUND : <span class="chemical">Tacrolimus</span> ointment is increasingly used for anti - inflammatory treatment of sensitive areas such as the face , and recent observations indicate that the treatment is effective in <span class="chemical">steroid</span> - aggravated rosacea and perioral dermatitis . 