This is basically a more natural (and less risky!) version of your Sun-In experiment from high school. Use a piece of lemon to lightly "paint" highlights onto your head — try focusing on small sections at the crown of your head and the pieces that frame your face. Alternatively, mix two tablespoons of lemon juice in a cup of warm water and apply to your strands as an all-over mask. Then, sit outside and let your hair dry in the sun, letting the heat activate the lemon. Be sure to follow up with a nourishing treatment, like a coconut oil mask, as the fruit juice may aggravate dry hair. After all, you're putting citric acid on it!