First, read the English article below.

Since dark spots can be caused by a number of different factors, learning about the different types will give you a head start when it comes to figuring out how to get rid of them. Here are the three different types of hyperpigmentation:   Lentigines. These are dark spots caused by exposure to UV rays from the sun. 90 percent of people over the age of 60 have them, but many much younger men and women have sun-related dark spots as well. The spots appear scattered in no particular pattern.  Melasma. This type of dark spots is caused by hormonal fluctuations. Women might see darker splotches appear on their cheeks during times when their hormones are in flux, like during pregnancy or menopause. It's also a side effect of birth control pills and hormone therapy treatments. Melasma can also occur as a result of thyroid dysfunction.  Post-inflammatory hyperpigmentation (PIH). These are dark spots that occur as a result of trauma to the skin, which can be caused by psoriasis, burns, acne, and certain skin care treatments that are hard on the skin. Once you know what you're dealing with, you'll be able to choose a course of treatment and start making lifestyle changes to prevent more dark spots from showing up. Ask yourself these questions to determine what's behind your dark spots:  Do you frequently use a tanning bed or go tanning in the sun? If you tend to get high sun exposure and you don't wear much sunscreen, you might have valentines. Topical treatments and avoidance of sun exposure are the best way to get rid of this type of hyperpigmentation. Do you have a current medical condition for which you're on medication? Are you pregnant, on birth control, or taking hormone therapy? It's possible you have melanoma. This can be difficult to treat, but there are certain methods that can make a difference. Have you had severe acne, plastic surgery, or other long-term skin conditions? You could have PIH, which responds well to topical treatments and may go away with time. The dermatologist will have a special... 

Now, please write a short abstract for it in Vietnamese. Abstract:
Tìm hiểu về các loại vết thâm khác nhau. Tìm ra nguyên nhân gây ra vết thâm của bạn. Đi khám bác sĩ da liễu để chẩn đoán.