My left ear periodically crusts on the inside?

Eczema: I suspect the most common cause of this is simple eczema, but some skin cancers can behave this way as well. I saw a young woman recently who simply had dirt build up in the ear canal that looked just like this. So the best answer is to have your ear looked at by a doctor, who can usually tell with nothing more than simply taking a look with their trained eyes as to what is the next step for you.

Various causes: Might be otitis externa (ear canal infection) or eczema (as other doc suggested) or seborrheic dermatitis, which can affect ear canals as well as pinna & external auditory meatus (although usually both sides are affected). Anti-dandruff shampoos & antifungal creams (lamisil) can help. If pain is involved, see fp or ent.