Hold your guinea pig on your lap, and gently lift up one ear at a time. All your guinea pigs’ ears should be free from crust and white marks. If there are any white marks then this could indicate a fungal infection, and your guinea pig will need to see a vet. If your guinea pigs' hair looks a little strange between its eyes and its ears, then this could mean that your pet is suffering from mites, which you will want to treat promptly to minimize their discomfort.
Have a gentle look at your guinea pigs' ears to check for problems
If your guinea pig’s ears are just generally dirty then you can wash them with a bit of guinea pig shampoo. Simply lather up the shampoo in your hands and gently rub it onto their ears and underneath them. If you are using a generic guinea pig shampoo rather than a mite one then take care not to get any in their ear canal, as you won’t be able to rinse it without risking getting water into the canal (if it is a mite shampoo, be sure to follow their instructions on ear-washing). Once it’s all nicely lathered, using your finger, smooth a bit of water onto the lather to rinse it off. Do this several times until all the lather has been washed out.