Certain chemical properties make an acid dangerous......For e.g., sulphuric acid has the property of absorbing water. Thus when it spills on the body, it can cause severe burns. Nitric acid similarly is an oxidizing agent. It reacts violently with the skin, muscles and bones to cause lethal damage. Certain other organic acids like citric acid, malic acid, acetic acid (in little concentrations) are not harmful and are edible. They are found in fruits.