Does eating a small piece of skin, smaller than a quarter of a fingernail, break one's fast?

It is not permissible for a fasting person to introduce anything into their stomach, whether food, drink, or medicine, regardless of whether it is beneficial or harmful. This is agreed upon by the four Imams. Swallowing things that are not ordinarily eaten, such as pebbles, dirt, or metals, invalidates the fast by consensus. However, if a fasting person swallows something unintentionally or without deliberation, their fast is valid, and there is nothing upon them.