I bet it that hardly will you see a lady today who has not changed in her physical appearance due to bleaching. It is so hard that some girls cannot be asked their throwback picture because of the differences in terms of complexion. Previous decades, bleaching was bound to women only but in this current time some men are even more into the act than women.
Bleaching is the use of some chemicals to whiten the dark parts or the whole body to give a toned result. It is usually popular with dark coloured people, and the fair ones use it to tone certain body parts. Using this chemicals to bleach and whiten the skin can cause serious harm after persistent and heavy usage. It is best advised to use natural or organic products to achieve this result.
If the bleaching is carried out with good products it could be worth it, but there is nothing altered without a side effects, so bleaching has side effects, and most people that bleach know this things but still go ahead and to them, i am surprised!
Harmful skin bleaching can result in the following:

Dark grey spots
Premarure aging of the skin
It causes cancer of the skin
Skin disorder (Skin inflammatory, Acne)
Skin begins to thin due to the bleaching of the upper dermal tissue of the skin.
Dark knuckles and elbow
Increased weight and increment in appetite
Abnormal loss of bony tissue resulting in fragile porous bones attributable to a lack of calcium, which is very common in bleaching women above 50.
Kidney disease or even damage and Neurological disorder caused by high concentration of mercury in those creams and soaps.
Body Odour: I remember sitting close to a women that bleached her skin, and after swaeting profusely the stench that was oozing from her was seriously bad.
Uneven coloration of the skin
Skin burns
Slow or even no healing of injuries: this is caused because the upper dermal layer of the skin has been peeled off by this bleaching agent or creams.
Causes stretch marks: believe me having strech marks is not as a result of using a bleaching cream but when you see some particular strech marks you will know they are caused by this act.

The side effects listed above may be visible immediately while some are obvious after a long usage of these bleaching creams.
source: http://www.omonaijanews.com/2016/10/health-implications-of-bleaching-skin.html