Article in English: The scent of authentic perfumes is complex and intricately constructed. While smell can be a difficulty measure of authenticity, those who know the perfume's scent can often sniff out a counterfeit. Authentic perfumes will have three layers of scents that reveal themselves over time, consisting of top, middle and base notes. This complexity ensures that the scent is varied and multidimensional, allowing the scent to change from the initial application until complete skin absorption. Fake perfumes will have one dimensional fragrance layer and it will often have an "off" smell after only a short time of wearing it. Authentic perfumes have had a lot of work put into creating the different notes in the perfume. They will use a mixture of scents derived from natural products and synthetic products. Cheap perfumes tend to be completely synthetic and therefore lack the complexity of layered perfumes created with natural ingredients. An imitation perfume will initially smell similar but you will usually find that the authentic perfumes outlast their imitators in terms of longevity and effectiveness, which makes them better value in the long run. Opened bottles of authentic perfumes should retain their scents from six to 18 months. Citrus-based scents generally deteriorate around the six month mark, whereas floral-based scents should maintain until 18 months. Cheap opened bottles of perfume will lose their scents in a matter of weeks or a couple months. When researching the perfume you’re about to purchase, it’s important to know whether it’s supposed to have a ‘single note,’ or a complex scent. Single note perfumes contain only the top notes, so a lack of middle and base notes doesn’t always indicate a counterfeit. When checking the authenticity of a single note perfume, pay attention to whether the scent smells strange and if the scent matches up with the description listed on the manufacturer’s website. You should only test out the perfume once you’ve examined the packaging and analyzed the scent beforehand. Be...

Summary in Vietnamese:
Hiểu được sự phức tạp của nước hoa thật. Biết các tầng hương. Phân biệt nguyên liệu tổng hợp và nguyên liệu tự nhiên. Chú ý đến tuổi thọ của nước hoa. Biết loại nước hoa bạn chọn có bao nhiêu tầng hương. Thử nước hoa.