How Long Does a Serum Last After Opening? Signs It Has Turned

An opened serum lasts for the period shown by its PAO symbol, the open-jar icon marked with a number of months. Use it within that time from first opening, provided it remains within its expiry date and has been stored as directed. Stop using a serum if its smell, colour, texture or consistency changes, or if the packaging is damaged. Separation that does not blend back after gentle shaking is another clear sign to replace it.

Check the PAO symbol before relying on the calendar

The most reliable guide is the Period After Opening, or PAO, symbol on the product packaging. It appears as a small open jar with a number followed by M, indicating the number of months the formula is intended to be used after opening. Write the opening date on the carton or bottle when you first use a serum, then count forward using the stated PAO period. This is more accurate than trying to remember when a product was purchased. Also check the printed expiry date where one is provided. Use the earlier of the two dates: the expiry date or the end of the PAO period. A sealed product and an opened product have different storage lives, because opening introduces air and repeated contact with the applicator and surrounding environment.

The clearest signs that a serum has turned

A serum that has turned usually gives visible or noticeable clues. Stop using it if the colour has changed, particularly if it has become darker, cloudy or uneven. An altered scent is another important sign: a formula that smells sharp, sour, stale or distinctly different from when first opened should be replaced. Texture matters too. Discard a serum that becomes unusually watery, grainy, lumpy, sticky or difficult to spread. Some formulas can show slight settling, but a separated product should return to an even consistency after gentle shaking. If it remains split into layers, do not use it. Leakage, a cracked bottle, a damaged pump or a cap that no longer closes properly also compromises the product’s condition and calls for replacement.

Storage habits that protect an opened serum

Keep serums tightly closed immediately after use and store them in a cool, dry place away from direct sunlight. A bathroom shelf beside a steamy shower is not an ideal location, as repeated heat and humidity can affect the formula and packaging over time. Avoid leaving skincare in a sunny windowsill, a hot car or near a radiator. Use clean, dry hands when handling a bottle, dropper or cap. Do not touch the dropper directly to skin, fingers or other products, then return it to the bottle. That simple habit keeps the applicator cleaner between uses. Always replace the cap securely and avoid transferring a serum into another container. The original packaging is designed to hold the formula and display its batch, expiry and PAO information.

Why formula changes matter more than a product’s age alone

An opened serum does not automatically become unusable simply because time has passed, but its stated PAO period remains the firm usage limit. Before that point, inspect the formula each time if anything seems different. Changes in appearance, scent or feel signal that the product is no longer in the condition intended for use. Do not try to correct a changed serum by mixing it with another product, adding water or using it only on a different area of the body. Replace it instead. This approach is particularly useful for active-led routines, where consistency matters from application to application. Keep one simple record of opening dates for products in regular rotation. It prevents several half-used bottles from being opened at once and makes it easier to finish products within their stated use periods.

Using Renoviq London serums within a tidy routine

Renoviq London serums are supplied in 30 ml formats, so a clear opening-date habit is useful when building a focused routine. The GHK-Cu — Copper Tripeptide Firming Serum is designated for PM use, while the PDRN — Polynucleotide Repair Serum is designated for AM/PM use. Check each bottle and its outer packaging for the applicable PAO and expiry information, then store it closed, cool and away from direct light. Keep the dropper clean and avoid allowing it to touch the skin before returning it to the bottle. If a serum develops a changed colour, smell or texture, stop using it rather than continuing to the end of the bottle. A product’s condition always takes priority over avoiding waste.