Synthol, or Site Enhancement Oil (SEO), does not provide true muscle growth. It creates an immediate, artificial increase in volume by physically pooling a foreign substance within the muscle tissue. The total duration of the cosmetic effect depends on how long the body takes to process each ingredient and the permanent structural changes that the foreign material causes.
Defining Site Enhancement Oils
Site Enhancement Oils are substances injected directly into specific muscles to temporarily increase their apparent size and shape. Synthol is a recognized SEO, typically consisting of three main components: oil, a solvent, and a painkiller. The mixture is usually composed of about 85% oil, with the remaining 15% split between a local anesthetic like lidocaine and an alcohol such as benzyl alcohol.
The oil component, often medium-chain triglycerides (MCT), is the bulking agent responsible for the immediate volume increase. When injected, the oil creates a depot that inflates the muscle fascia, creating the illusion of a larger muscle. Since these oils are foreign to muscle tissue, they trigger a significant reaction from the body’s immune system.
The Immediate Breakdown of Non-Oil Ingredients
The non-oil components have a very short lifespan and do not contribute to the long-term presence of the injection. The solvent, typically benzyl alcohol, functions as a preservative, while lidocaine is included to reduce the pain of the injection itself. These substances are metabolized and cleared from the body relatively quickly.
Lidocaine is rapidly metabolized by the liver. Benzyl alcohol is also processed and excreted within a matter of hours to a few days, depending on the volume injected. These temporary components are gone almost immediately, leaving only the oil to create the volume and the resulting tissue damage.
The Metabolism and Variable Duration of the Oil
The duration of the injected oil is highly variable, representing the temporary phase of the cosmetic effect. The body recognizes the oil as a foreign body and attempts to isolate and manage it. This response involves immune cells, such as macrophages, which attempt to break down or encapsulate the lipid material.
The persistence of the oil depends on its chemical structure, the total volume injected, and the specific injection site. Medium-chain triglycerides (MCTs) are more easily metabolized than non-biodegradable oils like paraffin, but the process is still slow. The oil depot can persist for several months to a few years before the volume from the unprocessed oil is substantially reduced. Complete absorption is rare, and remnants often remain much longer.
Tissue Response and Permanent Structural Changes
While the oil may eventually be partially metabolized or dispersed, the long-term effect of Synthol comes from the body’s reaction to its presence. The foreign oil triggers a chronic inflammatory response that leads to permanent structural changes within the muscle tissue. The body attempts to wall off the foreign substance, resulting in the formation of scar tissue, known as fibrosis, and hard nodules called foreign body granulomas.
Fibrosis causes the injected area to become hardened and lose elasticity, which can impair muscle function and mobility. The resulting mass of scar tissue and encapsulated oil, sometimes referred to as an “oleoma,” ultimately maintains the artificial size long after the original oil has dissipated. The cosmetic effect created by the body’s defensive reaction persists indefinitely, even when the original oil is no longer the primary source of the volume.