How are x rays harmful?

(excerpted from Howstuffworks.com) X-rays are a form of ionizing radiation. When normal light hits an atom, it can't change the atom in any significant way. But when an X-ray hits an atom, it can knock electrons off the atom to create an ion, an electrically-charged atom. Free electrons then collide with other atoms to create more ions. An ion's electrical charge can lead to unnatural chemical reactions inside cells. Among other things, the charge can break DNA chains. A cell with a broken strand of DNA will either die or the DNA will develop a mutation. If a lot of cells die, the body can develop various diseases. If the DNA mutates, a cell may become cancerous, and this cancer may spread. If the mutation is in a sperm or an egg cell, it may lead to birth defects. Because of all these risks, doctors use X-rays sparingly today. They are helpful in that x-radiation helps diagnose and treat illnesses in humans, pets and other animals. It is also an important part of scientific research, agriculture and countless industrial uses, such as the inspection of welds in construction, car manufacturing and aircraft maintenance.