Londoners are being warned to throw out old makeup.
The warning comes after research revealed that up to 90 per cent of used beauty products could be contaminated with potentially harmful bacteria.
Dr Conal Perrett, consultant dermatologist at The Devonshire Clinic in London, said: "People often keep Halloween makeup from one year to the next without checking whether it's still suitable to use.
"Unlike products in our everyday makeup bags, face paints and special-effects cosmetics can spend months sitting in cupboards or drawers, and we may forget when they were first opened."
The study found that between 79 and 90 per cent of tested cosmetics—including mascara, eyeliner, lipstick, and makeup sponges—contained bacteria such as E. coli and Staphylococcus aureus.
Nearly all makeup sponges tested (93 per cent) had never been cleaned.
Dr Perrett is advising Londoners to inspect their makeup bags before the festive season, noting that expired or poorly stored products can increase the risk of skin irritation and infection.
He said: "Previously opened cosmetics can deteriorate over time, particularly if they've been handled repeatedly or stored incorrectly.
"Applying contaminated makeup may lead to irritation or infection, especially when products are used close to the eyes or on already sensitive skin."
Contamination isn’t always visible, and changes in smell, colour, or texture may indicate that a product has gone off.
The warning is particularly relevant in the lead-up to Christmas, when long-wearing makeup and glitter are more commonly used.
Dr Perrett offered five key checks to reduce the risk of skin reactions.
The first is to check expiry dates before reusing old makeup.
He said: "Before applying products from last year, check their expiry information and the period-after-opening symbol, where provided.
"This usually appears as an open jar with a number followed by the letter 'M', indicating how many months the product is recommended for use after opening."
He also advised against sharing makeup on nights out, which can transfer microorganisms between users.
Dr Perrett said: "Always use clean applicators and avoid dipping dirty brushes or sponges into products.
"Extra care should be taken with anything being applied around the eyes, as this is a particularly sensitive area."
Caution is also needed when trying new or unfamiliar products.
He said: "A small test can help identify some reactions, but it doesn't guarantee that a product won't cause an allergy or irritation.
"If you notice itching, burning, redness or swelling, remove the product immediately and avoid using it again.
"People with known cosmetic allergies should be especially cautious."
He recommended removing makeup as soon as it becomes uncomfortable.
Dr Perrett said: "There isn't one universal time limit for how long Halloween makeup can safely stay on the skin, as this depends on the product and the individual's skin.
"Always follow the manufacturer's instructions and remove the makeup promptly if your skin starts to feel uncomfortable or irritated."
Proper removal after a night out is essential to avoid irritation.
Dr Perrett said: "Never sleep in Halloween makeup.
"Use a suitable makeup remover according to the product's instructions, followed by a gentle facial cleanser to remove any remaining residue.
"Try to avoid harsh scrubbing, particularly around delicate areas such as the eyes.
"Once your skin is clean, a gentle moisturiser can help relieve dryness and support the skin barrier."
If a reaction occurs, Dr Perrett advises stopping use immediately and removing the product gently.
He said: "Avoid applying more cosmetics or using harsh exfoliating treatments, as these could make the reaction worse.
"Mild irritation may settle once the triggering product has been removed, but if symptoms persist or worsen, it's important to seek medical advice.
"Significant swelling, particularly around the eyes, or signs of infection should be assessed promptly."
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