Nasal lesions?

[Wicky]

Looks like a virus or poison ivy in people. My friend's TWH, 9 years old, green broke. I didn't seen it yesterday, today he did fine with ground work but under saddle on the trail (he hasn't done a lot of that) he was tossing his head and acting anxious. We inspected his tack, I thought his noseband needed to be let out a hole as it was pressing on the poll. Then I saw these lesions. They are not painful. They are only on one side, with a few on the lip. I could not see anything in his mouth. He has no fever and otherwise seems OK - appetite, eyes, behavior (other than on the trail).

We will email the photos to the vet, but don't expect a response until tomorrow. Any thoughts? TIA!