Hypodermic Needles Types

hypodermic needle

The word hypodermic is derived from two Greek words, hypo and dermic. Hypo means under, and dermic means skin.

What is a Hypodermic Needle?

Hypodermic needles are medical tools that go under the skin or enter the skin. They are commonly known as Sharps. Hypodermic needles are quite skinny. Moreover, their shapes are hollow tube-like and have sharp tips.

Background of Hypodermic Needle

It is named as hypodermic needle because there was a surgeon who discovered the term hypodermic in 1858. He invented this unique word to define and elaborate on the term injection. He was Charles Hunter, a great surgeon from London.

Structure/ design of Hypodermic Needle


The hypodermal needles have three parts.

Hub: this part is made of polypropylene, and it fits on the top of the syringe.

Cannula: the cannula is a hollow tube-like long needle that is made of stainless steel.

Cap: it is usually made of PP and used to protect the cannula from contamination.

Hypodermic needle
Hypodermic needle

Different components, such as a plunger, a cap, a needle, and a barrel, are used to develop a syringe.

The Gauge of The Needle

The needle’s gauge refers to the inner measurement or the hollow part of the needle.  The needle’s diameter is measured with a Birmingham gauge (Sub iron wire gauge). In hypodermic needles, the gauge and length of the needles are inversely proportionate to each other. When the gauge increases, the length of the needle decreases. The 16g gauge needle will have a 40mm length, and the 30g gauge needle will have an 8mm length.  

needle size
Needle size

The 25g to 30g gauge needles are commonly used in aesthetics clinics for dermatological procedures such as anti-wrinkle injections and Botox.

Types of Hypodermic Needles

Generally, there are four main types of hypodermic needles, depending upon their usage.

  1. Intramuscular injection
  2. Intradermal injection
  3. Subcutaneous injection
  4. Intravenous injection

Differences among the Types of Hypodermic Needles and Their Functions:

The Type of injectionFunctionGaugeNeedle length
Intramuscular injectionIt delivers medicine directly into the muscles.Varies between20g – 29g13 mm to 16 mm
Intradermal injectionIt is used to deliver substance just beneath the dermis. It is preferably used to test skin allergies.Varies between25g to 30g8mm to 13mm
Subcutaneous injection It is used to inject medicine in the subcutaneous layer between skin and muscles, for example, insulin in diabetes patients.Varies between25g to 30g1/2” – 5/8” or 4mm to 8mm.
Intravenous injection It is used to inject directly into the veinsVaries between20g and 25g1/2” or longer

Uses of Different Types of Hypodermic Needles

As mentioned above, different types of hypodermic needles are used for other functions. Here are the details of the uses of each of the four types of hypodermic needles.

Intramuscular injection

This type of hypodermic needle is used for delivering medicines directly into the muscles. While injecting any substance, the needle is placed at an angle of 90 degrees with the skin. This type of needle is most commonly long in size. Hence, a gauge of 20g to 23g will work perfectly for these needles. But some practitioners also like to use 25g to 29g gauge sizes. The length of an intramuscular injection needle is usually between 13mm to 16mm.

Intramuscular Injection 23G
Intramuscular Injection 23G

Intradermal injection

Intradermal injections are used where the needle needs to be injected just under the dermis, below the upper layer, or epidermis of the skin. The most common uses of these injections are tuberculin skin testing, allergy testing, and injecting local anesthesia. A 25g to 30g g gauge is preferably used while administering an intradermal injection. The width of the needle is usually small, 0.5mm to 0.3mm, and the length varies between 8mm to 13mm. An angle of 10 degrees is made with the skin when the intradermal needle is injected.

Intradermal Injection 27G
Intradermal Injection 27G

Subcutaneous injection 

The term subcutaneous means under the skin. This type of hypodermic needle is used to deliver medicine into a layer of tissues called the subcutaneous layer present between skin and muscles. These injections are well known for injecting insulin in patients suffering from diabetes. Medicine delivered with subcutaneous injections is absorbed more slowly. Sometimes it may take 24 hours for the absorption. The preferred gauge size for these injections is 25g to 30g, and the usual needle length is 4mm to 8mm.

Subcutaneous Injection 25G
Subcutaneous Injection 25G

Intravenous injection 

These injections are used to inject medicine directly into the veins, and the medicine enters the bloodstream. Hence, absorption is quick. These injections are one of the most common health practices all around the world. They are used in emergency cases such as heart attacks, poisoning, or stroke. The size of the needle gauge for intravenous injections varies between 20g and 25g.

Intravenous Catheter 21G
Intravenous Catheter 21G

General Uses of Hypodermic Needles:

  • These needles are used for the speedy delivery of substances.
  • Hypodermic needles are commonly used with syringes to inject the substances inside the body, such as liquid medicine or drugs or saline solution, or to extract fluids from the body, such as blood.
  • The hypodermic needle plays a significant role in those research where hygienic conditions are required. Using hypodermic needles for the prevention of contamination during the inoculation process (a process in which artificial immunity is induced in the subject) has been proven effective.
  • These needles reduce the chances of contamination due to two reasons. One reason is that the hypodermic needle’s surface is smooth, so the airborne pathogens cannot trap on its surface. The second reason is their surface is very sharp. So, the diameter of the hole that resulted while puncturing the membrane is very tiny, and the microbes cannot contaminate the subject.

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