There are many factors that can cause your lips to go dark like some listed below and should be avoided.
Excessive smoking – The nicotine is the main culprit causing lips to darken or discolor
Extreme intake of Coffee - Excess consumption of coffee can turn lips dark in addition to staining your teeth. Same goes for tea.
Sun Exposure – Make sure to use lip balm with SPF 15 before getting out in the sun as lips contain an increased amount of melanin pigment causing the lips to visibly tan
Licking lips – Making your lips wet actually dries them out leading to injuries and darkening of the lips.
Dehydration – Lips are distressed when you are not drinking enough water. The recommended 2-3 litres of water should be taken throughout the day to keep your body hydrated and lips moisturized.
Lip Products - If you've been using your lip products for more than two years, its time to throw them away. It’s always better to use products from reputed makers and keep a check on product expiry.
Turmeric Powder – Scrub your lips with turmeric powder mixed with some whip cream to achieve lighter lips. The whip cream will also leave your lips moisturized.
Sugar - Mix sugar with a little bit of olive or almond oil and massage your lips. This will remove dead cells and dry skin from your lips and improve blood circulation.
Honey – Apply and leave it overnight for soft and pink lips.
Lemon – Its commonly used to lighten the dark areas like the elbows and knees, same goes for your lips too. Like honey , lemon can also be applied and left overnight for best results.
Glycerin – Massaging regularly with glycerin makes your lips soft and pink.
Ice cubes – Using ice cubes perks up your lips by blood circulation leaving it looking fresh.
Until next - Stay Blessed and Beautiful !