In addition to other functions for beauty like perfume, nail and hair care, cosmetics are now used for skin protection, lightening, moisturizing, eradicating acne, and anti-aging [1]. Cosmetics are no longer merely used to enhance the appearance of the skin; they are gradually being infused with active pharmaceutical ingredients (APIs), giving rise to "cosmeceuticals" [2]. According to the report released by MDPI in 2022, cosmetics prescriptions account for 40% of the global dermatology prescriptions. This demonstrates that people are looking for personal care items that provide numerous advantages with little effort [3].

Cosmetic formulas must be both aesthetically pleasing and practical [4]. For instance, using scent and essential oils might lessen the psychological stress caused by the COVID-19 epidemic, which led to a rise in demand for such goods [5]. In order to improve drug delivery routes and drug resistance, high safety nanotechnology was widely used to optimize drug function, particularly the skin distribution and creation of insoluble medicines [6]. One of the first industries to use nanotechnological principles in product creation was the cosmetics sector [7], [8]. More than 500 registered products could enhance drug delivery while preserving skin integrity [9]. However, several people voiced worries over the potential risks of coming into touch with human skin, including irritation from the addition of excipients, and human skin sensitivity or systemic exposure problems [10], [11]. These flaws may be fixed by using simple and effective nanocrystals.

Drug nanocrystals (NCs), a type of nanoparticle with a particle size distribution ranging from 1 to 1000 nm, consisting of pure drug without a carrier or any additional polymers, and requiring only a minimal surfactant (below the critical micelle concentration) for stabilization [12], [13]. In topical delivery, inactive keratinocytes and intercellular lipids form a thick and strong stratum corneum (SC) barrier. The main pathway for drug transdermal absorption is to infiltrate these components, which then pass through and are transported [14]. Only a small number of drugs with specific properties, such as logP= 1–3, molecular weight < 500 Da, or with low melting point (<200 °C), are able to hit this target. Therefore, SC is the main determinant of the skin barrier and the main obstacle limiting the rate of transdermal absorption. NCs have a straightforward structure, a high drug loading capacity, and a sizable relative surface area. These characteristics enable them to create a high concentration gradient between formulation and skin, more easily pass through the cuticle, and minimizing the associated toxicity (primary skin irritation index was zero) and boosting patient compliance and bioavailability [15], [16]. Considering the issue of systemic exposure, although there may be gray areas in the passive skin penetration ability of extremely small particles, available evidence suggests that the existing nanomaterials do not result in systemic exposure [11]. Moreover, compared with other formulations, the preparation skills of NCs are also simpler. Therefore, high-throughput screening of APIs was identified as a perfect application for NCs technology [17].

In terms of beauty, Juvedical® age-decoder cream of rutin by Juvena and Cellular Serum Platinum Rare of hesperidin by La Prairie were the first skin-protective cosmetics based on nanosuspensions of poorly soluble antioxidants to be released on the market in 2007 [18]. The form of NCs provides a contemporary perspective for drug development and application. However, since 2000, the development of nanocrystalline products approved by FDA has been slow, which shows that this field has broad prospects and exists many challenges [19].

The main objective of this review is to explore the potential of drug NCs for cosmetic and dermatological defense. Their advantages, preparation methods and different prevailing systems of carrier-loaded NCs were discussed. NCs with different drug components allow a variety of efficacy to be explored and their experimental effects were evaluated, also suggesting vacancies for research in related directions. Finally, the current status and challenges of stability and safety of NCs were stated and future perspectives were provided.