Factors such as the injection site, type, needle size, speed, amount and type of medicine, and any bodily structures in the way of the needle all affect the pain that comes with any injection. Variances in any of these factors make shots hurt to different degrees, according to InteliHealth.
Injections with a deeper needle that go into the muscle tend to cause more pain than the shorter needles that just go under the skin. When injections target a sensitive spot that has more nerve fibers, such as the hand, they hurt more than shots that go into areas with fewer fibers, such as the buttocks. The more medicine an injection contains, the more stretching the tissue endures, so more pain is involved, states InteliHealth.
Swift injections cause increased pressure on the tissue and can produce more pain. Some medicines, such as those with potassium, irritate the tissues more than others and can cause discomfort. When hospital patients receive intravenous potassium, it tends to sting as it courses through the veins. Some bodily structures, such as the lining of bones, the surface of the skin and certain nerves, are very sensitive, and injections that focus on those areas hurt more. The diameter of a needle affects pain levels as well, as a larger size damages more tissue and aggravates more nerve fibers, notes InteliHealth