Many things from Acne to rubbing of a wetsuit
Breast Milk
The herpes virus causes cold sores.
A few causes of sores on dogs backs that bleed are anemia, blood pressure, or dog lice. Dog lice irritate the skin causing oozing sores and crusty ear tips.
Te herpes virus causes cold sores.
No it causes itchyness.
Sex
There are a number of different unpleasant scalp disorders that can cause open sores. Some of the most likely illnesses include ringworm, psoriasis, and a bacterial infection. All of these can be treated by a physician.
Sounds like a flea bed spot bathe her with flea shampoo and treat with neosporin if she can`t reach to lick it off
staph
Sneezing. look it up....
FYI canaker sores are not related to oral herpes (the virus that causes cold sores). See related link for some remedies.
Impetigo causes weeping sores, its the 'weeping' that is contagious. Be it via skin to skin contact, a towel or virtually anything. When the sores are fully scabbed they are not contagious, its only the liquid inside the sores that is contagious.