30499
The degree of skin hydration is regulated by the gradient in water activity across the membrane , which in turn depends on the water activity of the formulation in contact with the skin membrane .
 None
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities:  
Answer:
 None