It has been a long time since the first sunglasses appeared. These "eye-protecting items" entered more widespread use at the beginning of 20th century, at which time glasses were not fashion items yet. They were worn exclusively for their function, which is, to block undesired light rays. In the second half of the twentieth century everything changed, as sunglasses became a fashion item. The function of the glasses was not solely important anymore, as it also became significant how they suited you and influenced your overall appearance.
Sunglasses quickly became a staple of various Hollywood stars. The movie stars realized that, apart from making them look good as well as protecting their eyes, glasses could also contribute to how other people saw them (i.e. the actors). Remember Marilyn Monroe during 1950's, with sunglasses playing an important role in her image of a sex symbol. James Dean was also popular during this period, and glasses helped him achieve the macho status. Both these stars wore easily recognizable glasses which over time became their trademark.
Each star has their fans who will go out of their way to look like their idols. It didn't take long for fashion companies to realize and take advantage of this situation. They began hiring various stars to wear their sunglasses when they appeared in public. This method became known as secret branding and achieved a tremendous success. During 1970's sunglasses became a global product.
Today one is able to buy a pair of sunglasses virtually on every corner: in boutiques, supermarkets, pharmacies, gas stations, markets, or online shops. It seems incredible that merely seventy years ago Foster Grant was selling the first serially produced sunglasses in Atlantic City.
Just as it was expected, sunglasses have become a huge business. Every year fashion houses launch new assortments of sunglasses designed to please (and sometimes surprise) the fans of these products.
Because of the need to present something new every year, the designers of sunglasses mix already well-known styles to create new ones: urban, vintage, retro, nerd...
We can say that sunglasses have become part of our everyday life and will probably remain with us for many-many years (to our great joy).