Fruit acids including citric acid from lemons are good for your skin in that they help dissolve dirt and oils. But using lemon directly on your skin can actually burn your skin and make it more susceptible to burning in the sun. To get the benefits of citric acid on the skin without risking burning definitely don't apply it to the skin for more than 5 minutes at a time and do not go out in the sun without sun protection after you've used lemon on your skin. If you are looking for the benefits of citric acid from lemon on the skin, make sure you're using the natural fruit of an organic lemon and not lemon juice, which can be a concentrate or a blend of juices that may not have the same benefits to the skin. But again remember if you plan on applying the citric acid of lemon directly to the skin you absolutely have to be diligent about sun protection.