The main "contributor" to the color of our skin is the pigment melanin. The more melanin, the darker the skin. If melanin is not completely evenly distributed in the skin, the skin tone/color is uneven. Hypopigmentations are areas where there is less melanin than elsewhere and hyperpigmentations are areas where there is more melanin than elsewhere.
Melanin is produced upon sun exposure because it is our natural protection – melanin absorbs the ultraviolet rays and thus prevents DNA damage by the sun. Dark skinned individuals are much better protected against sun damage.
Melanin is also often produced as a reaction of the skin to an injury (even without sun exposure). Such as post-inflammatory hyperpigmentation in acne, burns etc.
Melanin is produced by melanocyte cells. The cells are at the bottom of the epidermis, which resides approx. 0.2 mm into the skin.
If the hyperpigmentation is shallow, it is relatively easy to solve it.
If the membrane between the epidermis and the dermis is damaged, melanocytes or melanin gets deep into the skin and that is very difficult to solve (such as in dermal Melasma).
In some cases, the uneven production/distribution of melanin is hormonally related. For example in Chloasma, which typically appears in pregnancy.
Pigmentations also tends to re-occur upon sun exposure. You must avoid the sun as much as you can and always use a sunscreen.
You should definitely use Tretinoin cream (we sell it). It evens out the color of the skin.
Start using a 0.5 mm regular dermaroller, twice or three times a week. On the days when you do not roll, apply Tretinoin.
If you get no improvement in 6 months, it means that the pigmentation is deep and you should use a 1 mm regular roller and a Hydroquinone cream.
You can use a dermaroller to enhance the penetration of hydroquinone into the dermis but do not do it for a prolonged time. The best protocol is 3 month on, 1 month off.
Concerning the hypopigmentation, dermarolling/needling often "wakes up" the melanocytes, increasing their activity or enables the migration of melanocytes from the surrounding skin into the hypopigmented spots.