It has an approximate composition of SeS2, with individual rings varying in composition, such as Se4S4 and Se2S6.
Selenium disulfide has been used in shampoo as an antidandruff agent, an inhibitor in polymer chemistry, a glass dye, and a reducing agent in fireworks.Selenium trioxide may be synthesized by dehydrating selenic acid, H2SeO4, which is itself produced by the oxidation of selenium dioxide with hydrogen peroxide:

  
    
      
        
          
            SeO
            
              2
            
            
              
            
          
          +
          
            H
            
              2
            
            
              
            
          
          
            O
            
              2
            
            
              
            
          
          ⟶
          
            H
            
              2
            
            
              
            
          
          
            SeO
            
              4
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {SeO2 + H2O2 -> H2SeO4}}}
  Hot, concentrated selenic acid can react with gold to form gold(III) selenate.