I have been using this product for some time now with no problems until this week. One of my guinea pigs who is 950g in weight has developed a reaction at the site of application. The skin became red and has worsened over a number of days. Today she began scratching and was very uncomfortable. I took her to the vets who gave her a steroid injection and some steroid cream to calm the skin. I have had no problems with my other two guinea pigs using this product.