The darker complexion of your neck may be because you don't wash your neck as often as you wash your face.
Also, Aging and sun exposure are the main causes of dark discoloration on the neck. Other causes are diabetes, genetics, polycystic ovary syndrome, poor hygiene, and sudden weight loss or weight gain.
This skin pigmentation condition is known as acanthosis nigricans. This is neither an infection, nor contagious.
There are many natural remedies to reduce the discoloration of skin around the neck.
Step 1: Steaming
Dip a towel in hot water and squeeze extra water. Rub the towel on the neck and scrub. This tip is to reduce dark patches from the neck and steam it at the same time. Repeat this method also reduces the discoloration and fat settled around the neck.
Step 2: Exfoliating
Take some sea salt and mix with olive oil. The oil will help in getting rid of dry skin, dandruff and frizzy hair. Dip a cotton ball into this mix and apply all over your neck in circular motions.
Step 3: Whitening
Make a thick paste of 1 tbls of olive oil, 1tbls Sandalwood powder and 1-2 tbls of 'Golden Milk' (Breastmilk). Apply it for 30 minutes. This tip will help to get a fairer neck complexion naturally.
Source: House Of Healthy Food