dirty nose

Hi guys. so I just noticed my female Guinea has black stuff inside her nose which I cleaned and It came out easily. she doesn’t have a runny nose but this black stuff comes up again and again and I am not sure what’s it. I have attached a photo of the nose which can help to understand it...

I am a fairly new owner and I do not know everything about Guinea pigs. My one pig Totoro has green crust around her left nostril, and occasionally seems to breath a bit heavy. That could be because i turn on the heater in my room but, she also sneezes, and tries to wipe her nose. I do not know...