Dark spots on combs

[AODonnell]

A few of our girls have some small dark spots on their combs but also their nostrils? Is it just dirt from there dirt baths? Or do we think it is something more serious?

 

[AODonnell]

I can post more pictures if needed. I am a first year chicken owner and want to make sure I take the best care possible of my girls. I did try and google it but there are so many different things that I thought I would ask fellow chicken lovers instead.