Tea Tree oil/ Eucalyptus/Thieves - this includes: tea tree shampoo, tea tree oil, tea tree sprays and anything tea tree. Even Candles inhaled can harm your hedgehog! This can be fatal in as little as one dose or application. It causes renal, liver and complete organ failure.
Essential Oils: I have been advised that oils that are considered "hot" are toxic to hedgehogs. Oils that are considered hot: Cassia, Cinnamon Bark, Clove, Hyssop, Lemongrass, Ocotea, Oregano, Peppermint, Thieves, and Thyme. These are often contained in blends. Anything you put in the air your hedgehog will breathe and can be harmful!
Ivermectin (Injection or Oral ) - Used by veterinarians to treat mites. Due to the high concentration factor Ivermectin can be very difficult to properly dose and can be fatal in as little as one dose or application.
Polysporin and Neosporin Pain Relief or Extra Strength - Regular original Polysporin/Neopsporin are safe to use. Any other formulas are toxic.
Read the labels on foods and avoid them if the products contain any of the following:
BHA (butylated hydroxyanisole)
BHT (butylated hydroxytoluene) -"Toxic" may not be the right word here, but the following artificial preservatives in pet food are suspected to cause serious health issues in animals including cancer, kidney disease, birth defects, liver disease, and so on.
Toxic plants http://www.aspca.org/pet-care/poison-control/plants
Cedar Shavings or anything with Cedar in it. (*soft woods produce oils that can be toxic. We do not recommend any wood products to be used with hedgehogs unless properly sealed)