Injuries can be the result of heat, chemicals, or sun exposure. Until then, keep the area clean and do not scratch it. The application of aloe vera or honey can help to relieve the scar. With time, it will become less noticeable, but be careful as scars are slow to vanish. It is not enough to wear a hat in the sun, make sure you also avoid getting darkened by it. 

If you happen to have a high fever with lip blisters and during pregnancy you can't use medicine, rest easy. These come from a virus mostly. Try petroleum jelly ointments or aloe vera to help in wound healing and to keep the area moist. Also, press a cold pack a couple of times a day. Don't forget to drink lots of water and have enough sleep for the body to strengthen and overpower the virus.

Dark skin patches and acne can occur due to sun exposure, hormonal changes, or clogged pores. To improve your skin, use gentle cleansers, keep your skin moisturized, and avoid harsh products. Drink plenty of water, eat healthy food, and resist picking at acne to prevent scarring. Also, protect your skin from the sun to reduce further darkening.

You might have a medical condition named acanthosis nigricans. It can sometimes cause the lower face to be darker than the rest. It's not dangerous but could be a sign of something more serious, like insulin resistance, that is happening inside your body. You can fix this by eating cleaner, being active, and maintaining skin health. Furthermore, consume a lot of water. 

You suffered from a pimple on your cheek that is currently a scar, which is very common. The skin may leave a mark after the healing of a pimple. Whenever skin tries to fix itself these scars form. To make the spot where it is blended with your natural complexion, use remedies such as lotions containing retinol or vitamin C.