Misconception: For optimal hydration, it is recommended to moisturise within three minutes of bathing.

According to dermatology and allergy guidelines, experts agree on recommending patients to apply the moisturising cream as soon as possible after their daily bath, when the skin is still damp and, ideally, within 3 minutes following the bath to prevent and improve water loss, by restoring the skin barrier. However, the evidence supporting this recommendation is limited.

A 2009 study evaluated four different bathing and moisturising regimes, and their effect on skin hydration over a 90-minute period in 10 subjects, 5 of whom had atopic dermatitis. The regimes consisted of:

1. 10 minutes of bathing alone without the application of an emollient.

2. 10 minutes of bathing followed by an immediate application of an emollient.

3. 10 minutes of bathing and delayed application (30 minutes later).

4. Application of emollient alone.

The study reported that bathing followed by the application of an emollient significantly increased the hydration level of the epidermis, considerably higher than the baseline. It also found that there were no statistical differences in the average hydration state between applying a moisturising cream immediately after bathing and delayed application, that is, 30 minutes later. A similar observation was also reported in another more recent study.

In 2002, a study measured the hydration level of the stratum corneum and the transepidermal water loss (TEWL) at different times (30, 60, 90, 120, and 180 minutes). Although the hydration level of the stratum corneum increased and the TEWL decreased after the application of a moisturising cream, they found no significant difference between the skin areas moisturised immediately and those moisturised later. These results are consistent with those of the previous study on the effectiveness of moisturising creams.

Similarly, a third study conducted on 60 healthy volunteers (30 women and 30 men) reported comparable results. They compared the moisturising effects of a moisturising cream in terms of dosage, frequency, and timing of application. The water content in the stratum corneum at the test sites was compared between different application times: either immediately after bathing (within 5 minutes) or 90 minutes later. Compared to the control site, the application of a moisturising cream increased the water content in the stratum corneum at different application times, measured twelve hours after bathing. However, the results did not show a significant difference between the sites where the moisturising cream had been applied immediately after and 90 minutes after bathing.

Therefore, applying a moisturising cream immediately after bathing is ideal for the health of the skin barrier, but it is also possible to apply it up to 30 minutes afterwards. These results suggest that the timing of the moisturiser application does not impact its hydrating effect. However, the advantage of immediate hydration after bathing is to reduce the duration in which the skin is dry. This period, characterised by a drop in the hydration level of the stratum corneum and a rapid increase in TEWL, could potentially lead to the formation of lesions in the epidermal barrier and an exacerbation in patients with atopic dermatitis and psoriasis.

However, further studies are required with larger sample sizes and longer follow-up durations, while also considering washing/bathing conditions. Indeed, in the various studies mentioned, subjects merely rinsed their forearms or legs for 30 seconds to 10 minutes with tap water without soap in order to eliminate sebum or sweat residues on the skin. Yet, in real life, people generally use cleansing products during their bath. The type of cleanser, the duration of the bath, and the water temperature can affect the skin barrier function, which may result in differences in the hydration effect.

On the other hand, these studies highlight once again the benefits ofregular use of moisturising creams in the skin care routine, even for those with healthy skin, ensuring that the barrier remains intact. Indeed, the application of an emollient at this stage limits the evaporation of water present in the epidermis, thus preventing dryness.