There are several reasons for dark lips. I am going to share some of them. 

CAUSES OF DARK LIPS

Let’s discuss the first - allergic reaction to lips. Some allergic reactions to products like lipstick or lip balm can cause pigmented contact cheilitis making the lips darker than usual. 

The second type of allergy can be triggered by the application or hair dye for your facial hair.

No one can ever think that Green tea can also cause allergy to lips; in few cases due to the presence of Nickel in it. 

If you observe any allergic reaction to cosmetics like lip balm, lipstick or any hair dyes throw them away. It would be best if you visit a dermatologist for medicated and suitable brand products for you.

Avoid nickel-containing products. Choose a well-branded lip balm that has SPF 15 or SPF 20.

Drink at least 8-10 glasses of water every day.  

Avoid licking and smacking of your lips. 

Vitamin B12 deficiencies can be corrected by providing weekly injections or by pills to make your lips look healthier. 

HOME REMEDIES

Few home remedies:

1) Lime is known to have many health benefits. It is good to treat your lips by using one teaspoon of fresh lime juice with one tablespoon of honey and by adding 1 tbsp of glycerin. Apply this mixture on your lips before bedtime. Wash your lips the next morning.

BENEFITS OF LEMON FOR LIPS
Take a juicy slice of lemon and dip it in sugar then gently rub it on your lips. Leave it overnight and wash it the next day.

2) Add one tablespoon of milk with one tablespoon of turmeric to make a fine paste. Gently apply this paste on your lips, let it sit for 5-10 minutes, and rinse with plain water.

Gently massage your lips with few drops of almond oil, olive oil or mustard oil now and then.  

Now it’s time to discuss some effective treatment.

Treatments will be beneficial when compared to home remedies. 

TREATMENT OPTIONS

Based on the condition of your lips, we can plan creams containing Hydroquin, Kojiquin, Arbutin, or glycolic acid. 

Mild chemical peels for lightening of your lips once every 2-3 weeks will help. 6-10 sessions of peels might be required. 

Q-switch Laser Treatment is the best solution for lightening your lips. The laser light mainly targets the melanin and reduces the darkness. 4-6 sessions of laser are required once in every 3-4 weeks

Hyaluronic acid fillers reduce the lip pigment by hydrating the lips and provide excellent contouring to the lips making it look natural. 

Micropigmentation of lips with suitable colours gives even shade of colour to the lips.

Fractional lasers to improve the collagen production to the lips making it look healthy is suitable.