Hello
retinol does not lighten skin per se , it reduces dark appearance by exfoliating skin and if u don't take proper sun protection it may darken further due to tanning
HQ can be used for a maximum of 12 weeks without side effects and not advisable in lichen planus pigmentosus
Next Steps
consult a dermatologist for proper treatment in form of tablets and prescription creams
Health Tips
strict sunprotection - sunscreen, hat / scarf
avoid
vitamin c and other irritants on lichen planus pigmentosus