What is an Intradermal Injection?

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  • Written By: wiseGEEK Writer
  • Edited By: O. Wallace
  • Last Modified Date: 13 August 2019
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The intradermal injection is introduction via needle of tiny amounts of fluid into layers of skin. This is contrasted to a subcutaneous injection, where fluid is introduced underneath the skin layers. This type of injection has specific uses in the medical world. It’s often employed to check for allergies, but it may also be the kind of shot given for certain types of rabies treatments or to test for exposure to some elements, like tuberculosis. Different areas of the body may be chosen as the most appropriate injection sites depending on type of test, and in all, patients can expect slightly different experiences from these shots.

One difference with most types of the intradermal injection is needle size. The needle is narrow and short, and its length may help the person giving the shot from overshooting the mark and delivering medicine subcutaneously instead. While many shots are given perpendicular to the body part being injected, the syringe and needle in this type of injection are almost parallel to the body part. If a shot is given in the inside of the forearm, which is a common site, the syringe would be lined up nearly parallel to the forearm, better insuring that medicine gets between the layers of skin.


Another way the injection may be distinct from other types of shots is the way it is treated directly after the needle is removed. Rubbing or placing pressure on the shot site can change how well the body reacts to substance injected. To avoid this, a bandage is applied but, typically, putting pressure on the site is discouraged.

It’s noted by many that these shots tend to be more painful, and they last a little longer — an average of three to five seconds — because there are certain indicators that the target area has been reached. When medicine of any sort is given intradermally, its proximity to skin surface should show that blood is pooling under the skin, which may take a second or two. Without this characteristic, shots may need to be repeated because medicine may have been delivered subcutaneously by accident.

Many types of intradermal injection are given with the specific goal of looking for a skin reaction. With tuberculin tests, this reaction isn’t immediate, and patients will need to return to the physician in a set period of days to see if there is evidence of exposure to tuberculosis. For allergy testing, a reaction can be quite sudden and can occur within minutes of exposure to an allergy-causing substance.

This makes it highly necessary to have excellent monitoring of any patient receiving this form of allergy test. Many allergists also make certain that any injections given are done without exposure to medical equipment that contains latex, since this can corrupt testing if people are also allergic to it. Latex in the syringe or in gloves used during an injection are medically problematic and must be avoided.


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