Don't. Scar tissue has medically been found to lessen over time with the application of vitamin E - not citric acid. The cheapest and easiest way to apply Vitamin E is to get two bottles of the gel-caps - they are kind of a golden/amber color. Cut off the end of one and squeeze out a bit of the gel onto the scar area and rub it in. out of the other bottle take 2 in the morning and two in the evening - unless you are on other medications herbs/vitamins then read the precautions: http://www.healthline.com/multumcontent/vitamin-e?utm_medium=ask&utm_source=smart&utm_campaign=article_toc&utm_term=vitamin+E+precaution&ask_return=Vitamin+E#H7 Lemon contains Citric Acid, acid literally eats away the top layer of skin. On your hands this may not be such a problem considering that you most likely have calluses. On other parts of your body, say your upper thigh it may not be a problem. Your face on the other hand is exposed to air and sunlight - stripping away the protective layer of dead skin (we all have dead skin on the top layer) can lead to sensitivity to sunlight which can lead to cancers and other issues. Further your skin can be sensitive to the acid and over repeated application break out in a rash, develop discoloring (more than just an uneven tan) and it can lead to more scar tissue.