white cats ear!

My white cat Bella has a purple crusty bit on her right ear!

I check her ears all the time because they are pink and almost see through. She is an inside cat with some supervised outside time. She wears kitty sunscreen when she goes out unless its early morn or afternoon.

now my kitten bights her on the head every now and then so im wondering if its a bruise or cancer or what it is.

My question is how long should I monitor it before booking a vet apt if it does not go away??

Ill post a pic..

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I saw something just yesterday that even early morning and late afternoon sun can be bad, so would think you need to apply the sunscreen ANYTIME she goes outdoors.  That being said, since she does go outdoors, and white cats are susceptible to cancer on their ears, I would at least call my Vet and explain what is going on and see if they think she should be seen.  I thought normally it would effect the outer edges of their ears, but could be mistaken.  If she were my cat, I just wouldn't taken any chances.  She's beautiful, BTW. 

I would have a vet take a look at it too, better to be safe than sorry. On a lighter note, it could be just from the other cat and something minor. But for peace of mind I would take her in.

She is a beautiful cat.

Is it one ear or both ears?  If it fades in a couple of days then its probably sunburn, if it doesn't fade them more concerning....

And she IS beautiful!

Thanks all when I say out, she is usually in shade anyway and mostly sits in the door frame to scared to leave or is in and out (being scared of one noise or another or a leaf falling..haha) she has bad anxiety!
Oh wow..the vet did not even suggest sunscreen and then said if I were to use it that Id only need to during middle of the day.
My 3 indoor cats have white noses so they all get in on (and get a nice little face washy after)!
Well my kitten Lola (8months not really a kitten but she is THE kitten) bights the others on the ears all the time but I have never seen her leave a mark.
Ok..well maybe I will ring the vet. Sometimes I dont think they take me serious because I freak out about everything! I do have a naughty cat Jinx who was always up the vets as a kitten for things like eating little decorative rocks (out of a candle jar) etc. So sometimes I ring and Im sure they shrug me off lol