The spray is for the mites, can be used on the guineapig and in the cage, thats what it says on small pet select,says it totally safe for them, i usually just spray it about the hutch when i clean it just incase theres mites left on the base of the cage or on the sides, then i let it dry and put bedding in,
On another note that spot on i used which i had left over seemed to help especially since i applied it after a bath so most mites are gone for now, i only had enough for nova, but she had mites worst than the others and bathing got most mites off the others, numbers are down atleast! Happy me and happy piggies