Hi
A vet would be able to do some tests on the dandruff to find out if it is a parasite problem or something else. Guinea pigs can suffer from ringworm which is a fungal problem and would not be treated by ivermectin.
Cathy Wickenden BVet Med MRCVS
Barton Lodge Veterinary Centre
1 Midland Road, Hemel Hempstead, Hertfordshire, HP2 5BH
Tel: 01442 216048 24 hours
[
www.bartonlodgevets.co.uk]