There are many reasons why people may want to lighten their skin tone, but you have to be aware of the dangers of using some of the cheaper products on the market, or even those prescribed by a doctor. It's not just due to cultural reasons that people want lighter skin, but for many medical conditions as well.
I have personally become interested in the subject of skin whitening, after seeing a documentary on TV about how women in Asia in particular wish to make their skin lighter as a status symbol.
The reason behind this cultural trend, (and it's not just a trend, it goes back hundreds of years), is that in their culture, a woman with a fair complexion was seen as being more well off, and of a higher class, because they weren't tanned from working in the fields all day.
So, you have this perceived class difference of Indian, Chinese, and other Asian women (and men as well), based on the color of their skin, and many will do anything to try to alter their skin tone, and thus their status level.
I don't particularly agree with that cultural reason for whitening the skin, but it is a major thing, and people do try it in huge numbers, like western women try to get a tan.
The other reasons for people wanting to whiten the skin are that they actually have patches of discolored or darker skin that they want to even out.
Things such as hyper-pigmentation, or hypo-pigmentation, freckles, sun spots, birth marks, etc, and for all of these reasons, people need to find a product that can whiten the skin effectively, without causing any harsh, dangerous side effects.
Dangers Of Skin Whitening Products
I am getting this information from the Wikipedia page skin whitening, which is a fairly reputable source. Tretinion has been shown not to be very effective at all, and as such skin lightening creams that only contain this as an active ingredient are effectively fairly useless.
Hydroquinone was used by Michael Jackson to whiten his skin, and it is very effective, but can only be obtained in such a strong form by getting a prescription, and doctors are unlikely to prescribe it except in extreme cases.
Arbutin is found in the best skin lightening creams, because it is a natural source of hydroquinone, in a dosage that is not strong enough to cause any harmful side effects, and as such, it does not require a prescription, you can buy it online.
Vitamin C has also been shown to be a natural, but less effective skin lightening chemical, and so the stories of people using lemon and lime juice to lighten their skin tone are true, but you would need to use it for a long time, and use a lot of it for it to have a noticable effect.
I would suggest you check out the Wikipedia page if you want to read more about the different chemicals used in skin lightening products, and the dangers that some of them might have, and be sure to talk to your doctor, and do your research carefully, before purchasing any skin whitening products.