In case the word insecticide alarms readers let me hasten to add that it is also used to flavour food, hence it's safety for use upon guinea pigs. Massage the oil into the skin and leave on for two days then shampoo off. Leave for five days, repeat oil massage, leave for another two days, then shampoo off. Not only does this effectively kill the parasites, I find that it encourages the hair to grow much more quickly than can be expected in any of the conventional antiparasitic treatments. Occasionally, very badly infested animals need to be treated with the veterinary product Ivomectin by either skin application or injected subcutaneously.
Guinea pigs suffering fungal skin infestation have different symptoms altogether.
The hair has a greasy texture to it, there is a deep layer of gritty scurfing on the surface of the skin and the skin itself has a deep red flush to it. As with the parasitic infestation there can also be lesions caused through scratching. In the more advanced cases this scratching can sometimes lead to fitting and in these cases it may be necessary to treat systemically with the anti fungal drug, griseofulvin. I always use my formula of essential oils to treat this condition which seldom fails to deal with it. The oils are tea tree, lemon grass, patchouli, and lavender at a nine to one ratio with a carrier oil, ie, ten ml of the essential oils to one hundred of carrier oil.