Injection
Subcutaneous injection
A subcutaneous injection delivers a substance into the layer of fatty tissue just beneath the skin, above the muscle.
Subcutaneous describes a layer of the body, not a technique: it’s the tissue made mostly of fat that sits between the dermis (the deeper layer of skin) and the muscle underneath. A subcutaneous injection — abbreviated SubQ, SC, or SQ — is one delivered into that fatty layer rather than into muscle or directly into a blood vessel.
Where it sits in the body
Skin has layers: the epidermis on the outer surface, the dermis beneath it, and then the subcutaneous layer (also called the hypodermis) below that. Muscle sits underneath the subcutaneous layer. Because the fat layer is shallower than muscle, subcutaneous injections generally use a shorter needle than intramuscular ones — that’s a definitional fact about anatomy, not an instruction for how to give one.
Subcutaneous vs. intramuscular
- Subcutaneous (SubQ/SC/SQ) — into the fatty tissue just under the skin.
- Intramuscular (IM) — deeper, into the muscle itself.
The two routes differ in depth and tissue type, which is why product labeling distinguishes between them; absorption and other practical differences are a matter for the product label or a clinician, not something this glossary evaluates.
Where this fits in a routine
Terms like needle gauge and U-100 syringe markings describe the equipment associated with subcutaneous dosing, and site rotation is a separate practical topic — see the guide to rotating injection sites. None of this page substitutes for instructions from a healthcare professional or the product labeling for a specific compound.
Use it
Common questions
What does SubQ, SC, or SQ mean?
They are all abbreviations for "subcutaneous" — the layer of fatty tissue that sits between the dermis (skin) and the muscle. You may see any of the three used interchangeably on labels and in instructions.
Is subcutaneous the same as intramuscular?
No. Subcutaneous refers to the fat layer just under the skin, while intramuscular refers to the muscle tissue underneath that layer. They are different depths and different tissue types — see the intramuscular injection definition for the contrast.
How do I know if an injection is meant to be subcutaneous?
The product labeling or a healthcare professional specifies the intended route. This page defines the term only; it does not tell you which route applies to a specific product.
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