Poor nutrition is too often the reason behind weak hair, skin and nails. The key is often finding what your body is lacking. A common deficiency is iron, which results in thin, poorly growing hair. Other minerals such as zinc and biotin are also crucial yet commonly lacking in diet. Silica is great for connective tissue as well as collagen production in skin. It can aid the growth of hair and strengthen brittle nails. Alongside that, plenty of herbs can help nourish the blood and promote healthy growth.