Please help my guinea pig - large bare patch on the back

[Funnydonutsss]

My guineapig is the sweetest thing I have ever had and he got attack by another guineapig and he now has a dry bald patch on his back with dry skin, he is very itchy and he keeps pulling more hair out, he is very happy because is acting just like other pigies but I can't toutch him anywhere.
He also has a dry skin spot on his ear I really want him to be better I can see him like this!

It's a boy btw

 

[Funnydonutsss]

that is his bald spot

 

[Bill & Ted]

Your boy needs to see a vet to find out what this skin condition is. I doubt if this has anything to do with being attacked, it looks like ringworm which is very contagious (to humans too) and other piggies. Please see a vet ASAP as this won’t go away and needs treatment x
If you have more than one piggie then they all will probably need treatment

 

[VickiA]

It looks like ringworm. I’m linking the relevant guide. BUT it needs confirmation by a vet. Please don’t try to home treat on spec. Your piggy needs to see a vet for diagnosis and treatment. Your piggy is in distress if they won’t let you touch them anywhere.
Please read this guide very carefully as you need to protect yourself and other family members if it is ringworm Ringworm: Hygiene And Pictures

 

[Wiebke]

My guineapig is the sweetest thing I have ever had and he got attack by another guineapig and he now has a dry bald patch on his back with dry skin, he is very itchy and he keeps pulling more hair out, he is very happy because is acting just like other pigies but I can't toutch him anywhere.
He also has a dry skin spot on his ear I really want him to be better I can see him like this!

It's a boy btw

Hi!

Please have your guinea pig seen by a vet for a bad ringworm (fungal) skin infection.
They often start with a self-inflicted scabbing wound from a badly itching spot that is bitten or scratched open by the affected guinea pig and are not the result of an attack from another piggy. Those flakes look very much like a fungal skin infection. How long has your piggy had a bald spot?
Your piggy is not happy at all if any touch is painful; he is itching so badly that his pulling out hair and biting himself bloody even if he is still eating and acting normally.

Please be aware that ringworm is highly contagious and will spread to all guinea pigs, other pets and humans in contact with them. The period between infection and actual outbreak is 10-14 days.
With a prompt diagnosis and by following our very detailed hygiene measures, you can hopefully keep the outbreak confined to that single guinea pig, so act ASAP so you do not end up with a long running saga.
Do NOT treat on spec with cheap shop stuff as you can easily make the problem worse than better if you undertreat or treat for the wrong issue.

Please note that we can only make an educated guess, but we cannot replace a hands-on vet visit and a proper diagnosis.
Take the time to carefully read these two guides here. They also include information on your customer rights re. newly bought already infected guinea pigs as well as pictures of how an outbreak starts and runs and what you need to do to get on top of it once and for all.
What to check and look out for in new guinea pigs (vet checks, sexing, parasites&illness)
Ringworm: Hygiene And Pictures

All the best.