Considering your location, it is easy to understand why your skin can darken as easily as it does. The reason for your foot darkening when you use a toning cream on your face is probably because your footwear does not cover your feet and this exposes it to the sun, and since you are using a toning cream on the rest of your body, the contrast is quite stark. Again, considering your location, it would be advisable to check the ingredients of your toning cream for an agent called hydroquinone. This is one of the most effective bleaching agents around and has been used for centuries. Unfortunately, it is also carcinogenic. So, it would probably be a good idea to stop using it. Since a sudden change to the type of footwear you use doesn’t make sense, you can take some other measures to ensure that you don’t have to be stuck with this problem.
Skin darkening occurs due to a substance in the skin called melanin. This is essentially the skin pigment that gives human beings their various colors. When this melanin is exposed to ultraviolet radiation – like when you step out on a sunny day, the melanin undergoes a chemical reaction called oxidative stress. This is an incomplete oxidative reaction because of the low oxygen content in the skin, which causes the melanin to turn dark. The more the exposures, the darker the melanin gets. This entire process is also called skin tanning. Skin toning potions use agents that reverse the oxidative stress and return the melanin to its original state. This can be done with a substance like hydroquinone or even naturally with Vitamin C. There are also some remedies that you can take to suppress melanin production but this is not a good idea if you live in the tropics. This is because the melanin in your skin also protects you against skin damage from ultraviolet radiation by converting the radiation into harmless heat.
To bleach your skin naturally, you would require a vitamin C-rich solution. Strawberries are one of the richer sources of vitamin C but if this is too difficult to acquire where you are, you could just purchase a strawberry face wash over the counter as well. If even this is not possible, you can use guava, which is quite abundant in Nigeria. Combine this with some lemon juice and make a paste. Apply this to the skin that you want to bleach and you should see some results. You should also think of using sunscreen to protect yourself.