A few months ago, I used a hair curling cream that had been sitting at the back of my bathroom cabinet for ages. But, when my strands didn't do any of the things promised on the bottle (de-frizz, add shine, create curls), I realised I'd had it for four years

Rules of expiration
My curling cream had definitely gone past its best. Even though products can typically be kept unopened for three years, this decreases to about 18 months after it has been opened, according to Cindy Moser of Zotos International, a parent company to hair care brands like Bain de Terre. The shelf life of opened products is decreased by about 50 per cent because they come in contact with bacteria from skin or become diluted from drops of water.

To get the most out of your purchase, aim for products in spray containers which last longer even after opening.

'Products such as aerosols are sealed and don't run the risk of contamination or dilution so their shelf life is not shortened once opened,' explains Moser. When buying conditioners, opting for tubes instead of jars is also a good bet.

And, even if hair care items stay unopened, they expire after the industry standard of three years. 'Over time, oxidation, heat and even light can diminish the full potency of natural and organic ingredients,' says Pat Peterson, the executive director of research and development at Aveda.

Toss and forget
The best way to tell when a product is expired is by its texture and scent. Erin Anderson, a celebrity hair stylist, usually tosses her gels and creams six months after opening. But ultimately, she judges the product by how it looks. 'Creams will usually separate or curdle,' she says. 'A dark yellow colour is another sign that a product is past its prime.'

But even if you're not keeping track of the way every product in your bathroom cabinet originally smelled and looked, you should still be able to tell, says Moser. 'If the smell is unpleasant, such as a dirty or sour smell, it's a good indication,' she explains. The good news is that expired products aren't harmful to hair, with only a small chance of scalp irritation, says Fabian Lliguen, a stylist and owner of the Cocoon Hair Studio in New York.

And, regardless of irritation, many hair products (like my favourite curling cream) simply become ineffective without visible changes to texture and smell.

Label the goods
While exact expiry dates still aren't popping up on product labels, some companies have developed systems to help you keep track. At John Paul Mitchell Systems the recommended number of months a product should be used is printed on the hair products.

So, when it comes to what's in your bathroom cabinet, use products with caution. And if you don't already do so, get in the habit of labelling, or at least remember when you bought what.