The everyday items with unexpected expiration dates, from sunglasses to smoke detectors

Nine unassuming household products that have limited shelf lives

Due to dust, contaminants and insects, the efficacy of smoke detectors decreases over time. Getty Images

Expiration dates are a standard feature on a vast array of products, most noticeably on food and beverage packaging. The dates let the consumer know the item's shelf life to ensure food safety measures are met and to negate potential damaging side effects that can arise from consuming out-of-date or spoiled items.

Less well-known are the expiration dates of things used daily, such as child car seats, mascara and sunglasses, which experts recommend replacing after varying lengths of time as their effectiveness wanes.

Here are nine lesser-known products with an expiration date and how often to replace them.

Sunscreen

Shelf life: Three years

Sun protection creams expire, reducing their effectiveness and ability to protect skin from the sun's harmful UV rays. In the US, the Food and Drug Administration requires that sunscreen remain at its original strength for at least three years, although some formulas may have an earlier expiration date.

"Like the majority of your skincare products, SPF also comes with an expiry date," says Dr Aiza Jamil, consultant dermatologist at Healthpoint Abu Dhabi. "This is down to the formula, which contains important active ingredients and chemical UV protectors, which, after a certain length of time, can become less effective.

"With these ingredients no longer working at maximum level, our skin is less likely to be protected from UV damage. Not only this, but with ingredients degrading within the sunscreen, this can also cause allergic reactions, irritation, and bacterial growth."

Storing sunscreen out of direct sunlight can help it remain effective, including keeping it in the shade or a bag while out and about.

Bike helmets

Shelf life: Three to five years for high usage

Like bike tyres, helmets also wear down over time, particularly when used daily for rides and commutes. The hard foam, plastic and glue used in modern helmets can be degraded by the sweat and oils from the body and the sun's UV rays.

With a wide range of expiration dates across different brands, experts recommend changing helmets every three to five years for high usage and every five to 10 years for low.

Regular cleaning can prolong its effectiveness and durability, while any helmet with a crack, fissure or visible damage should be replaced immediately.

Child car seats

Shelf life: Around seven years

Along with the usual baby and child-centric wear and tear on a car seat, such as accidents and spillages, the average chair goes through a lot of stress during its years.

Children can be put in and out of a seat thousands of times, not to mention hot car temperatures in the summer and fluctuations throughout the seasons. Materials also wear down over time, reducing their effectiveness meaning parents should consider lifespan when reusing car seats for younger siblings.

Experts also advise not to use a car seat that has been in a moderate or severe crash due to the stress a collision might have on the materials.

Sunglasses

Shelf life: Two years

It’s unlikely a new pair of sunglasses will come with an expiration date. However, the lenses' effectiveness can degrade over time, making replacement essential, particularly in sunnier climes. Scientific research is thin on the ground, but prolonged exposure of sunglasses to UV rays as well as scratches on the lens, is understood to have a detrimental effect on the coating which provides UV protection.

Experts suggest looking for sunglasses with 400 UV, which offer UVA and UVB protection, and investing in a new pair every two years.

Medicine

Shelf life: Varies

While it can be tempting to keep unfinished medicines in the cupboard to use again, it is vital to adhere to the expiration dates on pharmaceuticals. Loss of effectiveness and potency, increased risk of side effects and microbial contamination are just a few of the issues which can arise from consuming out-of-date medicines.

"Over time, the active ingredients in medicines can break down or degrade due to various factors," says Dr Archana Prabakaran, general practitioner at Aster Speciality Clinic, Ajman.

"This chemical change can reduce the effectiveness of the medication or even render it useless. In some cases, expired medications can be harmful to the body. This is especially true for medications that contain potent or toxic substances."

Smoke detectors

Shelf life: Five to 10 years

The "replace by" date of a smoke detector is usually found on the back beside the serial number, with the length of time varying from brand to brand.

Smoke detectors have an expiration date because environmental factors can reduce the effectiveness of the sensors over time, such as their ability to sufficiently recognise an excess of smoke in the event of a fire.

The accumulation of dust, airborne contaminants, insects, and worn-out circuity can also contribute to a reduction in sensitivity.

Paint

Shelf life: Six months to four years

"Any item, whether natural or synthetic, has a shelf life which is dependent upon the surrounding environment," says Sairam Iyer, operations manager at Jotun Paints UAE. "The gradual disintegration of paint, whether via natural or chemical reactions, means expiry dates can vary from six months to four years, depending on the different paint types, formula, ingredients and storage."

Paints that have expired can dry out, become hardened and have a rancid smell, while an opened tin may be subject to bacterial contamination. On average, oil-based paints have a longer unopened shelf life than latex.

Mascara

Shelf life: Three to six months

Cosmetics have a short shelf life owing to the fact they are used daily and constantly come into contact with skin and environmental factors.

Experts suggest changing mascara every three months if used daily and six months if used occasionally due to bacteria transference from the eyelash to the wand and tube, which puts the user at risk of an eye infection or irritation as the bacteria builds up.

"Mascara should be changed every six months even if the expiry date indicates otherwise," says Margherita Lascala, a make-up artist at Beam, London. "Each time you use mascara, it gets exposed to air. This, coupled with the placement of the wand on your eyelashes, causes the mascara to become exposed to bacteria and contaminated with it."

Trainers

Shelf life: Every 480 to 800km

Like sunglasses, trainers don't come with an expiration date, so it's up to the owner to keep an eye out for wear and tear.

Trainers whose soles have become flattened through prolonged use will be less effective at protecting the foot and joints, leading to potential damage or injury as materials used for cushioning and support lose their effectiveness over time and distance.

Generally, running shoes should be replaced every 480 to 800km, says Susan Jacob, a physiotherapist at Aster Cedars Hospital and Clinic, Jebel Ali. She adds: "The range can vary based on factors like running style, body weight and the surface you run on. If you run frequently or are experiencing discomfort, you might need to replace them sooner."

Old trainers have reduced shock absorption, which affects support and performance, while new shoes should provide the right level of arch support for different foot types.