The phrase "alien substance" is correct and usable in written English.
It can be used in scientific or literary contexts to refer to a material that is foreign or not native to a particular environment or organism.
Example: "The researchers discovered an alien substance in the soil samples that had unusual chemical properties."
Alternatives: "foreign material" or "extraneous substance".
It's easy to think of them as naive non-westerners, unaware of the possible dangers of an alien substance.
I remember meeting tarmac again, and finding it an alien substance, even after only a few days away from roads.
In Ron Howard's 1985 movie, "Cocoon," some retirees regain their vigor and joie de vivre thanks to an alien substance brought by visitors from outer space.
When an alien substance enters the body, the immune system is able to recognize it as foreign because molecules on the surface of the antigen differ from those found in the body.
If I were suddenly to become a superhero as a result of contact with a mysterious alien substance, which is what happens to the heroes of Freedom Force, I would be relieved to find that it had happened to a few other people too so I could go to superhero support groups and discuss my new life.
Wikus eventually gets exposed to a powerful alien substance which begins transforming him into... one of them.
The most damaging particles are invisible to the eye and can evade the body's normal protective mechanisms, like tiny hairs in the nostrils and cells within the lungs designed to expel or destroy alien substances.
It seems that women are more susceptible to suffer from autoimmune diseases, and that environmental factors and alien substances may act as haptens and render autoantigens immunogenic.
This indicated that the Au/SiO2 particles were probably recognized as alien substances and were intensively trapped in the liver and the spleen.
This vendetta is enhanced by the appearance of the mysterious black alien symbiotic substance that bonds to Peter, resulting in the formation of a new, jet-black costume.
The most recent overview on threats to the biodiversity of the Baltic Sea includes the lists of the following 10 major categories: fisheries, maritime activities (including shipping), physical damage and disturbance, recreational activities, eutrophication, hazardous substances, alien species, noise pollution, hunting, and climate change [54].
