<s>[INST] I have a dark purple pea size lump behind my ear. It does not hurt to the touch and is the second time I have had it appear.  the first time, I thought it was a tick! I got it checked out, but the doctor didnt really have any info other than it possibly being a blister. Do you know what this is? [/INST] Hi, It could very well be blister or a Sebaceous cyst. They dont usually cause any problems but stay there and dont disappear. If they are poked they might get infected and might then require removal by a minor surgery. I suggest dont worry about it and keep it under close observation. If it throws any symptoms like pain or increase in size then you should see a Surgeon who can advice you accordingly.Take care,Dr Rishi, New Delhi, India. </s>