Please don't ignore them!!
They will only continue to get worse and they will cause sores on the skin underneath them. Boo came with serious eye boogers crusted on and by the time we finally worked them all the way off he had horrible sores on both sides of his nose.
We wash his face nearly every day now to keep the crude cleaned off.
If they are seriously bad you can use a Chamomile tea bag to moisten them with. Boil a cup of water with the tea bag in the microwave, steep the tea for a few minutes, don't press out all the water, but cool the tea bag so that it's warm but not hot to the touch. Gently hold the tea bag against the crude and let it soak it a bit. Then you can work it loose with a fine tooth comb. If it's really built up, like Boo's was, it may take several days to totally clean it off.