thank you for your query. a small abrasion on tip of the penis may occur due to injury while masturbating or having sex, and usually recover spontaneously. quadriderm cream (containing betamethasone, a steroid) may be used. however, since you are also having a sore foreskin and a couple of small blisters on the tip, it is advisable that you rule out any sexually transmitted disease (STD) first. If you are having an STD, then applying quadriderm without the correct antibiotic may worsen the infection. I would suggest you to visit some Dermatologist and STD specialist urgently for the same while avoiding self medication. If it turns out to be an STD, you need not be alarmed, it will get cured by a couple of doses of the right antibiotics that your specialist will prescribe. hope i ve been able to satisfy your query, please feel free to contact me for any further clarifications if needed. best of luck.