1. Introduction
Although it is best known as the source of a recreational drug, the
Cannabis sativa plant has a large variety of other uses, e.g., as an ingredient in food and cosmetics, a textile material, and a medicinal product [
1]. The cannabis plant contains various chemical compounds known as cannabinoids, which is a term that initially only encompassed those substances produced by the plant, namely, phytocannabinoids. One of these compounds is tetrahydrocannabinol (THC), which causes psychoactive effects known from the recreational use of cannabis. Moreover, endocannabinoids (endogenous cannabinoids) refer to cannabinoids that are naturally produced within the body as part of the endocannabinoid system, while synthetic cannabinoids are manufactured substances that have similar properties to phytocannabinoids [
2].
The phytocannabinoid cannabidiol (CBD) has been the focus of attention due to its neurological and anti-inflammatory effects [
3,
4,
5]. Products containing CBD are often sold over the counter, e.g., as dietary supplements, to circumvent the laws regulating medicinal products.
Substances derived from cannabis, such as hemp oil and other cannabis extracts, are becoming increasingly common ingredients in cosmetics [
6]. Recent studies have demonstrated the potential use of cannabinoids to treat dermatological conditions, such as pruritus, skin cancer, and inflammatory skin diseases [
7]. For instance, hemp oil is offered on the market as a cosmetic hair treatment, with product manufacturers claiming that the direct application of the oil can moisturise and protect hair, promote hair growth, and repair damaged hair. Despite the lack of scientific evidence supporting these claims, numerous online outlets sell these products, which range in composition from pure hemp oil to shampoos and similar hair treatments containing lower concentrations of hemp oil [
8].
EU cosmetics regulations state that all hemp-derived natural raw materials contained in cosmetics must be derived from
Cannabis sativa plant parts, including seeds, leaves, or leaves without tops, whereby the total THC content must not exceed 0.2%; notably, the flowering or fruiting parts of
Cannabis sativa generally feature higher THC concentrations. The use of nonfibrous cannabis material with an excess of 0.2% THC (e.g.,
Cannabis indica) is forbidden, and this limit of THC refers only to hemp plants—not to hemp-derived cosmetic ingredients [
9]. In contrast, UAE cosmetic regulations state that the manufacturer of any cosmetic product containing hemp oil (
Cannabis sativa seed oil) or cosmetic oil containing CBD (cannabidiol) must demonstrate that their finished cosmetic products are free from tetrahydrocannabinols by tetrahydrocannabinol content testing in municipal laboratories or accredited laboratories. However, despite these regulations, several cases of contaminated cosmetic products have occurred on the UAE market [
10]. For example, a survey of 100 cosmetics and other personal care products available in the UAE found that 13% and 5% of samples were contaminated by yeast/mould and aerobic mesophilic bacteria, respectively [
11]. Another study in the same context revealed that 13% (
n = 9) of the tested cosmetic and personal care products not only contained formaldehyde above the recommended levels but also did not state on the label that the product contained free formaldehyde or formaldehyde releasers [
12].
To the best of our knowledge, our study is the first to assess the quality of cannabinoid-based cosmetic products available on the UAE market. In particular, it aims to quantify the presence of undeclared tetrahydrocannabinol, specifically THC and THCA, in these products. The findings will contribute to ensuring compliance with current regulations and aid in the development of new methods for identifying adulterants in cannabinoid-based cosmetic protects with the aim of ensuring public safety.
4. Discussion
Despite a lack of research into the effectiveness of over-the-counter topical cannabinoid-based cosmetics, their availability on the market has recently increased. Manufacturers advertise these products as safe treatments for various skin conditions, such as acne, psoriasis, and atopic dermatitis (AD), or as a way to promote healthy hair. Nonetheless, the lack of scientific evidence on the safety and efficacy of these products remains a concern. Given this situation, the current study aimed to examine to what degree these products available on the UAE market contain undeclared tetrahydrocannabinol, specifically THCA and THC.
The current study found that the sampled products had an average tetrahydrocannabinol content of 0.011%. However, the regulatory regime of the UAE stipulates that cannabinoid-based products may contain no tetrahydrocannabinol chemicals, and the adulteration of these consumer products bears substantial risks that considerably outweigh any public health benefits.
Our study is the first to measure to what extent topical cannabinoid-based consumer products contain undeclared tetrahydrocannabinol, thereby contributing to the literature on the safety of cosmetic products containing cannabinoids. Previous research developed a method for detecting the constituents and metabolites of cannabis in hair, thereby allowing cannabis exposure to be determined [
12,
13,
14,
15,
16].
A study in the UK showed that using hemp oil to cosmetically treat hair can lead to the absorption of THC, cannabidiol (CBD), cannabinol (CBN), and, on rare occasions, even the metabolite 11-hydroxy-delta-9-tetrahydrocannabinol (THC-OH) [
8]. This study also demonstrated that when volunteers applied hemp oil to their hair, 89% were found to have absorbed one or more constituents of cannabis, while 33% had absorbed the three major constituents, namely, CBD, THC, and CBN [
8]. Moreover, in their study of (self-reported) heavy cannabis users, Taylor et al. found that 77% had traces of THC in their hair, 73% had CBN, and 19% had CBD [
17]. Similarly, Franz et al. found that THC-OH concentrations in participants’ hair varied between 0.05 and 37.6 pg/mg [
18].
The research indicates that exposure to high levels of undeclared tetrahydrocannabinol can adversely affect consumer health, particularly in the form of cannabinoid sensitisation or the development of a cannabinoid allergy, with symptoms ranging from mild to potentially fatal reactions. This sensitisation is particularly of concern because of cross-reactivity with similar substances, such as latex, tobacco, or alcoholic beverages derived from plants or other foods [
19]. There is also evidence of cannabis arteritis among young cannabis-consuming adults, which is a severe peripheral vascular disease that can cause a loss of limb use [
20]. Moreover, preclinical research has indicated that although cannabinoids can have antineoplastic effects, they might contribute to the early stages of malignant transformation [
21]. Based on the abovementioned evidence, there is a clear need to conduct thorough research into the effects of cannabinoid use and to ensure that these effects are used solely for the treatment of dermatological conditions.
Of particular concern is this study’s finding that cosmetic products meant to be left on tend to have a higher total tetrahydrocannabinol content than those that are rinsed off. This may be the result of most of the products tested here being marketed as treatments for atopic dermatitis and eczema. These dermatological conditions imply inflammatory dermatoses that can cause the skin barrier to weaken, meaning an increased risk of skin infection for consumers of cosmetic or personal care products adulterated with undeclared tetrahydrocannabinol. In addition, more vulnerable groups, such as the elderly, children below three years of age, and immunocompromised individuals, are particularly susceptible to the effects of adulterated cannabinoid-based products [
22]. Finally, products marketed as suitable for application near the eyes are a particular issue due to the fragility of periocular skin [
23].
This study has revealed that although cannabinoid-based cosmetics offer potential treatment methods for a variety of inflammatory conditions, there are still several areas of concern. For example, only limited research has demonstrated their efficacy and safety, with most data emerging from preliminary animal studies. In addition, the frequent adulteration of these products with undeclared tetrahydrocannabinol is an important issue. Therefore, it is strongly recommended that current regulations be revised and updated to ensure better compliance for cannabinoid-based cosmetic products. This result can be achieved through the following policies:
Producers of cannabinoid-based cosmetic products should provide a safety assessment report to provide evidence of the purity of all raw materials used in the manufacture.
The raw materials used to manufacture cannabinoid-based cosmetic products should undergo quality control testing and meet the agreed standards. Producers should also prevent contamination by controlling the validation process, implementing worker training, and reviewing and improving the cleaning process.
As part of the treatment programme, dermatologists should enquire about patients’ use of cannabinoid-based products; this policy is particularly crucial, given the unsubstantiated claims made by manufacturers as part of their marketing strategies.