Recomended treatment is 4 weeks on the face and six weeks elsewhere. You probably got to the worst of it but the problem will reoccur as it did with me. The harm you noticed is actually the process of killing the damaged cells. Good cells do not react to it. By stopping; the process stops and the problem will be free to spread again. I have heard of longer treatment times which need to be decided by your doctor. For me two weeks and then 4 weeks of treatment was not enough and I had to begin the process all over again as it came back and that is no fun either.   The most difficult question I have had to get answered is how long to treat it? I am on my third round which I'm hoping will do the job.   Try shopping around for the Efudex, or try a canadian pharmacy. I have seen the 40g tube for as low as $33.00 plus shipping.   Please note, that keratoses is a pre-cancerous condition which can in time metasticize into something more serious.