Everyone has heard of using lemon juice and laying out in the sun to streak your hair.
Lemon juice on its own will do nothing to your hair as far as color goes.When mixed with UVA/UVB rays from the sun lemon juice will have a lightening effect on the hair. This process takes about 5 hours sitting in the sun to work so make sure you use a good sunscreen!
Lemon juice is naturally acidic in nature. Alot of hair care products use citrus extracts to help balance the pH of hair.The natural pH of hair is around 5. pH is measured on a scale of 0 to 14 with 0 being extremely acid in nature and 14 being extremely alkali. A pH of 7 is considered neutral.Lemon Juice has a pH of about 2. So if your hair is on the alkali end of the pH scale, the acid will balance out the pH levels in your hair leaving it softer and more manageable.
However overuse of lemon juice will cause your pH levels to get out of whack and end up too acidic. This can leave your hair feeling dry and damaged.
Lightening with lemon juice works best on those with already light hair. If you use it on hair that is darker and that has red pigments in it, you can end up with brassy orange streaks because the lemon lightening system just isn't strong enough to break through the red molecules in your hair.
If you do choose to use lemon juice to lighten your hair, make sure you wash it out well and use a good conditioner that does NOT contain other citrus extracts to keep your pH levels in check.
Also avoid using heat on top of the lemon juice.That means no blow dryers, no flat or curling irons, nothing. Think of how as kids you used lemon juice as invisible ink.Once the lemon juice on the paper was held over a heat source, it turned brown and showed up for reading. It will do the same thing in your hair which totally defeats using lemon juice to lighten the hair.Plus it is nearly impossible to remove that brassy effect without resorting to bleach and harsh chemicals.
Products like Sun In have the same problem when heat is applied so use carefully and wisely washing thoroughly after your sun time lightening session.