Hi!
Lip pigmentation can be due to many reasons
1. Hereditary
2. Eczema
3. Smoking
4. Cosmetics
5. Sun exposure etc
6. Inflammatory skin conditions
Treatment can be done after finding the correct cause.
Next Steps
Show it to a dermatologist .
Get correct diagnosis and take treatment.
Last resort would be chemical peels and laser toning to lighten the lips
Health Tips
Use a lip balm with SPF like Sebamed SPF 15 or hydralips.