STERILE EO
STERILE EO is the marking for medical devices sterilised by ethylene oxide gassing. The gas acts by alkylating the nucleic acids of micro-organisms, killing bacteria, viruses, spores and fungi.
The process is governed by ISO 11135 and is preferred for products that cannot withstand high temperatures: single-use plastic instruments, complex polymer components and pre-packaged sterile disposables.
After EO sterilisation the product must undergo a degassing phase to reduce EO residues to toxicologically acceptable limits.
The sterility assurance level (SAL) for validated EO processes is typically 10⁻⁶, meaning that statistically no more than one non-sterile product per million product units is to be expected.
On packaging, the symbol for STERILE EO appears in accordance with ISO 15223-1 together with the expiry date of sterility.
Frequently asked questions
Why is ethylene oxide used to sterilise medical devices?
EO sterilisation is a low-temperature process, making it suitable for heat-sensitive materials such as plastics and polymers that cannot withstand steam sterilisation. The process is standardised in ISO 11135.
How can I identify an EO-sterilised product?
The packaging carries the STERILE EO symbol per ISO 15223-1, distinguishing EO-sterilised products from steam-sterilised (STERILE) and radiation-sterilised (STERILE R) products.
Are EO residues in sterilised products a health risk?
EO residues are toxicologically relevant and are assessed against limits in ISO 10993-7. Validated degassing processes ensure residue levels remain within permitted thresholds before product release.