Fungal Skin Problems
Fungal skin infections in guinea pigs can be far more serious than parasitic problems if they are not caught early, and treated quickly. As with most things in life, prevention is better than cure, and regular shampooing every 4 - 6 weeks can help to prevent skin problems from happening in the first place.
Fungal skin infections usually start off with "a bit of dandruff" on your guinea pig's skin. If the hair is gently tugged, it will come out easily and will have dry, flaky skin on the end. This is the stage at which to catch the problem and start treating it before it gets any worse.
Guinea pigs may become sensitive to your touch around the affected areas. This is particularly noticeable around the rump area.So, catch that "bit of dandruff" early, and treat it promptly before you end up with what could be a potentially fatal situation if the guinea pig starts fitting.
If your guinea has a very stubborn fungal infection, there are anti-fungal dips available from your vet. Please be aware that they are quite harsh on the skin. For systemic fungal infections, your guinea pig may need a course of Itrafungol. Again, see your vet for diagnosis and treatment.
Ringworm is also a fungal infection that guinea pigs can get, and often appears as a circular pattern of hair loss. This is not often seen in guineas, but great care is required if this has been diagnosed by your vet, as ringworm is easily spread between animals and humans, humans and humans and humans and animals.