Povidone Iodine does help for fungal, Lorna - in my own experience, anyhow! A few drops mixed with shampoo has worked very well for Saffron, she has ongoing trouble but the P.Iodine wash has cleared up a problem patch better than anything I have found yet.
As the others have said, do check with a good vet, but to me from the picture you posted it looks like a "fungal nose stripe". I did have a great link on it but I can't find it now, will keep searching! I had one sow with this for years, it caused no trouble but was removed/treated eventually. (It was not until I got to the CCT that she advised I deal with it, no other vet mentioned it!)
Gorgeous Guineas Lavender & Myrrh lotion is safe for use on faces and treats fungal, may be worth looking at.