Hi,
It is definitely not a good idea to apply lemon juice directly to the skin for whatever reasons: either to rejuvenate the skin or to lighten pigmentation.
This is because lemon juice is highly acidic at pH below 3. This highly acidic nature frequently causes skin irritation and even chemical burns, resulting in further skin injury and pigmentation.
Lemon juice also contains chemicals called furocoumarins which makes the skin more sensitive to UV exposure, leading to increased risk of sunburns and blotchy/streaky UV induced pigmentation.
Hope this helps.
