The Earth's Crust is like the skin of an apple. It is very thin in comparison to the other three layers. The crust is only about 3-5 miles (8 kilometers) thick under the oceans(oceanic crust) and about 25 miles (32 kilometers) thick under the continents (continental crust).
The problem behind your itchy skin might be insufficient vitamin intake. There are a number of vitamins that promote the hydration and healthiness of your skin. A shortage in these could trigger itchiness, dry skin and other skin conditions. Alternatively, an overdose of such vitamins might also lead to itchy skin.
As mentioned earlier, it is very uncommon to be deficient of biotin as it readily available in common foods. However, in cases of lack or deficiency, it can cause skin problems like dry skin, rash, dermatitis, psoriasis, and itchy skin. In addition to oral supplementation, there are topical products for skin use.