Everyone is Talking About: Double Shampooing
- TRI Princeton
- May 1
- 5 min read
Double shampooing is a trend that is gaining traction within health and beauty, but what is it and why would you do it? This short article will take a closer look at the trend of double shampooing and whether there are any risks of oil or protein stripping and the likelihood of subsequent hair damage.
Double shampooing involves cleansing the hair and scalp twice in the same sitting. It’s suggested that the first cleanse is to remove surface-level grime and dirt from everyday exposure to the environment, and the second is to remove build-up of other hair products, such as dry shampoo or dirt and oils, that are engrained more deeply. However, this approach seems at odds with another school of thought, which is to cleanse hair as little as possible to avoid stripping the hair of the natural oils (lipids).
To begin: why should I wash my hair?
Within a beauty routine, hair cleansing (or washing) to remove dirt is extremely common and has several important benefits:
Removal of sebum, which is secreted by the skin and scalp.
Removing sebum can lead to improved scalp health, for example by controlling Malassezia (formerly P. ovale) levels, a yeast that can lead to dandruff.
Ensuring hair growth and development is healthy.
Dandruff caused by build-up of oil of the scalp can impact upon the development and growth of new hair fibers, in some cases leading to compromised formation of pre-emergent hair and poor fiber formation.
Reducing inflammation.
Washing hair more often reduces levels of biomarkers for inflammation and can lead to improvements in scalp health, regardless of hair type.
Does washing my hair strip my hair of goodness?
Washing hair removes dirt or materials from the hair fiber, as well as other entities that might also be naturally present. A common worry is that cleansing removes hair lipids as well as proteins from the hair fiber, causing damage.
Cleansing and the impact on lipids
Hair lipids, although only contributing about 2–6% of hair’s overall weight, play a vital role in overall hair health, fulfilling a range of natural functions including both acting as a waterproof barrier and being a structural component within the hair matrix cells. As well as these vital biological roles, the presence or absence of lipids can also have a bearing on consumer perception, with the presence of lipids in and on the hair fiber influencing shine and hair feel. And there is science behind this consumer perception; research has shown that losing hair lipids causes hair to feel dry or unhealthy.
But there are more to hair lipids than meets the eye. Lipids are found in both the cuticle and cortical cell membrane complex and can be characterized as either exogeneous (deriving from sebaceous glands) or endogenous (deriving from hair matrix cells). When we talk about washing hair with shampoo, we’re usually referring to removal of surface lipids rather than those that are structural – and this has been shown to be true. A study by Procter and Gamble showed that when hair was washed daily, the levels of beneficial internal hair lipids remained the same, whereas on the hair surface there were fewer sebum lipids, fewer oxidised lipids, and hair had a lower greasy shine score. In fact, this study found that concerns about ‘overcleaning’ were unfounded, and overall satisfaction with hair and scalp condition was achieved when washing hair once daily, 5 to 6 days per week.
While, to the best of our knowledge, there haven’t been any studies into whether double-shampooing strips internal hair lipids from hair fibers, recent studies have shown that once daily washing does not have detrimental impact on the hair, and in some cases gives the user benefits. Extrapolating this forward, and in the absence of studies to show the contrary, it would be reasonable to assume that shampooing hair twice in one sitting would not negatively impact the hair fibers through stripping lipids.
Cleansing and the impact on proteins
Hair is comprised primarily of the keratin (approximately 80% w/w), which is a fibrous, structural protein. While to date there have not been many studies considering protein stripping from hair by surfactants, one study from de Cássia Comis Wagner and Joekes did consider the impact of washing hair with sodium dodecyl sulfate (SDS) upon hair protein levels. They noted that with increasing temperature, more protein was lost from the hair, which was exacerbated when hair was rubbed. They also noted that more damaged hair lost more protein. However, there were some limitations to this study, which may impact upon the extrapolation to real-life data and are important to note: hair fibers were submerged in 5% SDS solution for multiples of one hour, arguably much longer than would be expected in a domestic situation, and the temperatures tested were likely hotter than seen at home (e.g. 70 °C). Data referring how long hair fibers were rubbed was not provided. This means that while these results are still valid, their application within a domestic setting may be limited.
There’s more to shampoo than surfactants
However, while this article has thus far considered the impact of surfactants, there is more to a shampoo formulation than just these compounds. Within a shampoo there are commonly four main ingredients: surfactants, deposition (or conditioning) polymers, structuring polymers and viscosity modifiers. Each of these components has a different role, and all are required to allow the shampoo to carry out its function correctly during the different stages of the washing process. While the surfactant is concerned with removing dirt, the polymers are intended to act in a beneficial manner or to allow the shampoo to fulfil a particular function, for example by adding conditioners, reducing dandruff or adding ‘anti-frizz’ properties. This means that if any potential degradation of a hair fiber were caused by the surfactants, polymers could be added to the formulation to counteract this.
In terms of hair damage by double shampooing? The jury’s out, but it stands to reason that if the surfactant were to remove lipids or proteins, polymers to counteract this could be added, reducing any negative impacts.
But consider the environment…
When considering the impact of double-shampooing only on the hair fibers, it looks like there isn’t a negative impact on the hair lipids and hair properties – internal hair lipids are unaffected, only lipids on the surface of the hair that can lead to dandruff and inflammation are removed, and protein removal isn’t a massive concern. However, washing hair twice in one sitting comes with an unseen environmental impact: more product will be used by virtue of the fact that cleansing is being undertaken twice. The impacts of this will be felt both upstream and downstream of the consumer: more resources will be required for shampoo production, and arguably more water will be required during the hair washing process (which will also need treatment). Both of these outcomes have an environmental cost, which will largely be unseen by the consumer.
The take-home
While washing hair twice in one sitting doesn’t seem to have any negative impacts on hair there is arguably a hidden environmental cost. If hair feels clean after just one cleanse, it probably doesn’t need to be washed again. But, if you’ve been doing something where hair is covered in grime or doesn’t feel clean after the first wash, then there’s no harm rinsing and repeating.