With targeted pigmented areas, there are a couple of treatment options to be considered:
- Topical lightening creams
- Pigment Lasers
- Chemical peels
Home remedies like what you have mentioned actually do contain acids in its natural form, but you do have to be careful because overzealous application can also cause irritation to the skin and worsening of pigmentation.,
Inflammation (if any) to those areas also contributes to pigment formation and will have to be addressed as well.
Hope that helps.
All the best!