Agree, with
@HappyDuckie on it being pox.
Fowlpox is a common viral infection in poultry, that occurs in warmer temperatures, where mosquitos and other bugs are most likely to transmit the virus. Luckily, the cutaneous form, (which is the form that affects the bird's comb, and face), tends not to be harmful to the bird, and usually only causes irritation, and sometimes secondary infection of the tissue. The dipretic form, which affects the mouth, and throat, is more serious and can lead birds into an anorexic, dehydrated state due to the lesions inside the mouth, preventing eating/drinking.
If you're only seeing lesions on the face, simply applying an antibacterial ointment such as Neosporin, or an antiseptic such as iodine, or chlorhexidine a couple of times a day would be good to prevent infection of the surrounding tissue. Environmental measures such as disinfecting feeders, and waterers, and installing mosquito mesh around their pen often helps to prevent further spread of the virus. Additionally, some folks choose to administer vitamins, specifically A, as that is partially responsible for maintaining the health of the squamous epithelial cells that protect the other tissue from the pox lesions.
If you have a rather large flock, and a good portion is currently unaffected, you may consider vaccination, but the virus usually runs its course over a few weeks/month, and afterward, the birds seem to be immune to future infection of the virus.
