How do you choose which shampoo to buy? Do you take the advice of your hairdresser or believe the adverts you see in magazines or on television? Perhaps you just opt for the brand on special offer in the supermarket? Most importantly, does it make any difference?
The answer completely depends on what you are hoping to achieve. My recent study for BBC Two's Horizon programme found that in some cases the simple answer is that is doesn't matter which brand you choose or how much it costs. This is because all shampoos contain similar ingredients to clean your hair. Known as surfactants, they are the same compounds used in many other cleaning products such as washing-up liquid.
These compounds are excellent at removing dirt and grease through their unusual multi-functional nature. At one end of a surfactant, the molecule is hydrophilic, – it is content to be soluble in water – yet at the other end, it is hydrophobic and will attract oil and dirt.
When added to water, the molecules of surfactant spontaneously assemble into a spherical structure that captures any oil-based dirt inside the sphere, helping the grime to leave the surface of the hair. This is perfect for washing hair as the surfactant molecules within the shampoo mix with the water as you wash, then drag the dirt away as you rinse your hair.
If this is their only purpose, then shampoos – whatever they cost – are all the same. This was proven scientifically for the Horizon programme using two PhD students as volunteers who were instructed not to wash their hair for a week.
Samples of unwashed hair were collected and tested by washing in a range of shampoos and then analysed using microscopy to look closely at the surface of the hair to see if any dirt and oil remained. The study found that all samples, regardless of which shampoo was used or how much it cost, were equally clean after washing.
Is there a catch?
The cheapest shampoo (costing about £1 per bottle) left one student with a small static charge on the shafts of their hair, which quickly attracted dirt and dust back onto the surface. In this case, the hair would initially appear clean after washing, but dirt would soon find its way back onto the hair, making it a poor long-term cleanser. This might make it wise to avoid the very cheapest brand. That said, there was no difference between any samples from the mid-range shampoo and the much more expensive shampoo that cost more than £40 per bottle.
So what's the point in spending more money on a shampoo if they largely all clean your hair just as effectively? Well, it's all the other ingredients that you are really paying for, such as fragrances and extra conditioners. The ability to clean your hair, after all, is only part of the overall function of shampoo.
Consumers want to use a shampoo that has a good, thick texture and one that smells appealing as they wash their hair. Interestingly, we found that thicker products do not work any better than the thinner brands yet the general belief that there is a connection between thickness and quality encourages the industry to thicken their products.
These thickening compounds cost extra money and therefore increase the price – as do unique blends of unusual fragrances such as extracts from exotic plants and flowers. Often the more expensive shampoos also contain a variety of conditioning agents to help avoid static hair, and leave it more manageable, softer and easier to style.
But even if a shampoo does contain conditioner, you will also still need a separate conditioner as, anecdotally, often the best results are seen when a more expensive shampoo that contains conditioners is used alongside a separate conditioning treatment.
People buy shampoo for a whole variety of reasons. If you love a particular brand because it works for your hair – and it smells divine – there's no reason to switch. If you just want clean hair, however, then price doesn't matter and swapping brands could save you a small fortune in the long run.
Horizon's Hair Care Secrets is on BBC Two on Monday, January 23 at 9pm. It will also be available on BBC iPlayer.