Can you wear contacts when your eyes are red?

Not recommended. You should find out why your eyes are red first and take care of the problem whether it's an allergy, infection, or over use. If infection, for instance, the contact may worsen the infection. In any case, you may experience pain, burning, and tearing if the eyes are red.
You shouldnt. Red eyes can mean anything from contact lens overwear to a serious corneal infection. Discontinue contact lens use with any red eye and if there is no improvement, see an ophthalmologist.