Rescue pigs strange patch of hair

[muchiemul]

I have two rescue guinea pigs boars, fluffy and cookie, who both have a greasy patch of fur and a bit of flakey yellow skin underneath. What can this be?
I have washed and brushed them both as the hair was a bit matted to.
this was about a week ago and apart from the matting, the fur and skin is the same. does anyone know what this could be?:{

 

[clairelove]

is this on the end of their back? where a tail would be if they had one?

if so this is their greese gland and it sounds a little clogged up.

i use a little fairy liquid on this greese glad rub it in and wash it off x

 

[muchiemul]

Yes it is where a tail would be, Thanks I will try that!

 

[clairelove]

you may have to do it a few times over the next few days to get it clear x