As a kind of toxic and strongly carcinogenic substance, nitrosamines are likely to be present in the raw materials of cosmetics, or during the preparation, storage, and transportation processes. This would result in the potential hazard to the health of consumers. This paper carries out the study on nitrosamines. Firstly, the physical and chemical properties of nitrosamines as well as their types in cosmetics are introduced. Then, the formation reasons and possible reaction mechanisms of nitrosamines in cosmetics are summarized. Next, various detection methods of nitrosamines are concluded and compared. The legislation, norms, and standards for nitrosamines in cosmetics around the world are listed. Finally, the development trends of detection, supervision, and management for nitrosoamines in cosmetics are predicted.
Economic development and the pursuit of beauty make the cosmetics market vigorous, and cosmetics are essential for the peoples in their daily life. Due to the strong purchasing power, China has become the second largest market of cosmetics in the world. It has been reported by National Bureau of Statistics that the total retail sales of cosmetics of China in 2021 reached 402.6 billion yuan, increasing by 18.41% in comparison with 340 billion yuan in 2020. Hence, the average annual rate is higher than that of other countries. Moreover, the number of licensed cosmetics manufacturers is 5,400, and the number of products with legal licenses reaches up to 1.6 million. Hence, the cosmetics have a wider develop space in China . As is well known, cosmetics are a kind of mixture produced according to scientific formulations. During the processes of production, processing, storage and transportation, some harmful substances could be generated or brought into, thus posing a threat to the consumers’ health. Among them, nitrosamines are the common hazards with obvious carcinogenicity, as well as easily produced by the reaction between precursor secondary amine and nitrite. Simultaneously, the reaction can progress well under the natural conditions or in the human and animal bodies. They can enter our bodies via the respiratory tract, digestive tract, or skin. Moreover, not only can the long-term low dose cause cancer, but also a shock of higher dose can directly result in carcinogenesis . Therefore, the nitrosamines harm has undoubtedly been paid close attention to. Moreover, it is of great research significance and application value to know the sources, influence factors, formation mechanisms and detection methods of nitrosamines in cosmetics to effectively inhibit the formation of nitrosamines.
The nitrosamines have significant carcinogenicity, which is related to their chemical structures, physical and chemical properties, tissues and organs, metabolic process, etc. However, until now, the specific mechanism has still not been clear. The existing findings suggest that the increase of electron-withdrawing ability of hydrogen at α-C (R1 and R2) attached to ammonia nitrogen decreases the electron cloud and density of α-C and N-nitroso-group and increases the number of static charges. This would make the hydrogens on the carbon atom more reactive, and easily oxidized, decomposed, isomerized to alkyldiazohydroxides in vivo. As a highly active carcinogen, this compound can block DNA replication and induce gene mutation . Furthermore, some
researchers have found that the carcinogenicity of nitrosamines
might be related to the free radical activity. For example, Hirata et
al. have shown that the N-nitrosamine compounds in the tobacco
could induce the generation of reactive oxygen species, stimulate
the Wnt signal path, and thus resulting in the lung cancer.
All the countries issue the standards for the contents
of nitrosamines in cosmetics. However, there are still many
cosmetics with a lower content of nitrosamines, and then they
can’t be analyzed and detected at the present stage. Furthermore,
due to the complex raw materials and limited detection means,
the generation condition and formation mechanism are still
unknown, which further increases the difficulty to effectively
inhibit the content of nitrosamines in cosmetics. In this paper, the
types of nitrosamines, generation causes, reaction mechanisms,
detection means, regulations and standards in various countries are summarized, so as to provide the references for relevant manufacturers, consumers, supervisors, and researchers.
There are many types of nitrosamines in cosmetics (Figure
1), of which the most common one is N-Nitrosodiethanolamine
(NDELA). In 1997, the Food and Drug Administration (FDA)
first reported that the detection rate of NDELA in cosmetics was
up to 31% with the content of 1~130000 μg/kg [4,5]. In 1986,
2-isoctyl-4-(N-nitroso-N-methylamino) benzoic acid (NMPABAO)
was detected in the sunscreens, as well as a familiar type of
nitrosamine. Notably, with more attention to the cancer risk of
nitrosamines and the progress of detection technology, more than
300 types of nitrosamines have been detected in cosmetics. The
frequently detected ones are listed in Table 1.
Raw materials: Since nitrosamines were detected in
cosmetics in 1977 for the first time, most researchers regard
the raw materials as an import source of the nitrosamines. From
1980 to 1984, FDA detected 1 mg/kg of nitrosamines in about
30% cosmetics . Joo et al.  detected NDELA in multiple
raw materials of cosmetics (triethanolamine, trimethylamine,
coconut fatty acid diethanolamide, fatty acid chain alkanolamide,
and triethanolamine-dodecyl sulfate) with high-performance
Liquid Chromatography-tandem Mass Spectrometry (HPLCMS-
MS) method. Guo Huifang  analyzed the several typical
nitrogen-containing surfactants in cosmetics, such as coconolic
acid monoethanolamide (CMEA), cocoanut fatty acid n,
n-diethanolamide (CDEA), and castor oil acylthreonine sodium,
simultaneously, established an efficient and simple method to
detect the NDELA in nitrogen-containing surfactants.
In 2014, the detection limit and quantification limit of
volatile nitrosamines in ten types of cosmetics were determined
in China . However, the complex raw materials of cosmetics
could result in the increase of the types of hazards introducing
the nitrosamines. Cocoamidopropyl betaine (CAB) is common in
cosmetics, and widely used in washing products such as shower
gel, shampoo, and hand sanitizer. It has a quaternary ammonium
group with strong electronic induction, which makes the
carboxylic acid group attached to the quaternary nitrogen atom
always present in a salt-like group, and thus showing amphoteric
ions characteristics. Hence, CAB is a kind of better surfactant
. The synthesis of CAB includes three steps, that is, synthesis
of cocamidopropyl dimethylamine, neutralization between
chloroacetic acid aqueous solution and alkali, and synthesis of coir
amide propyl betaine, as shown in Figure 2.
Both the raw materials for synthetizing CAB and intermediate
products have the tertiary amine structure. Moreover, once the
tertiary amine structure contacts with the nitrosation reagents
such as nitrite and nitrate, the nitrification reaction would
occur. Therefore, there would possibly form a tiny amount of
nitrosamines during the synthesis process of CAB, resulting in the
potential risk of nitrosamines in the products.
Preparation process: In addition to the raw materials, the
preparation process of cosmetics is also an important source of
nitrosamines. Under the effect of nitrosification reagents, the
precursors (primary amine, secondary amine, and tertiary amine)
can form nitrosamine compounds. Among them, the secondary
amine is more prone to nitrosation reaction . At present, there
are many nitrosation reagents, i.e., HNO2, NO, NO2, N2O3, N2O4, NOX (X=Cl and Br), various nitrates, and nitrites. If the cosmetics contain diethanol amine DEA), triethanolamine (TEA), nitrosation agent, and fatty acid alkanolamide as the emulsifier or pH modifier,
there would form nitrosoamines under certain conditions .
As such, the formation mechanism relates with pH. Under acidic
conditions, HNO2 can directly react with amines, or two HNO2
molecules can react with each other to form N2O3 and H2O. Then,
N2O3 forms nitrosamine after one-step reaction. For example, the
nitrosation reaction of N, N-dimethylaniline can progress under
the acidic condition, and this reaction can be divided into two
steps (Figure 3). Firstly, the nitrous acid forms the nitrosyl cation
in an acidic environment. Subsequently, the nitrosyl cation attacks
the nitrogen atoms as the electrophile, thus forming the nitroso
cation intermediate of nitrogen. Then, according to the different
classifications of amine, the substituents attached to nitrogen
atom with positive charge of intermediate are different. When
the hydrogen atoms are attached to nitrogen atoms of primary
amine and secondary amine, they can be directly removed to
form nitrosamine. On the contrary, there are no hydrogen atoms
attached to the nitrogen atoms, so failing in dehydrogenation.
However, the dimethylamino is an active group, and the nitroso
cation can form C-Nitroso compound through the electrophilic
substitution on the para-position of the benzene ring .
Nitrosamines are relatively stable under non-acidic
conditions, whereas the resonant structure resulting from
conjugated effect between lone pair electrons and nitroso could
make the H attached to α-C easily oxidized. Moreover, as the
electron withdrawing group is attached toα-C, the electron cloud
densities of α-C and N-NO would be decreased. Simultaneously,
the H attached to α-C would be more active and easily be oxidized.
In 2002, CHOI et al.  have reported that NDMA could be
formed in the waste water with chloramine, and simultaneously,
they proposed the reaction mechanism (Figure 4). Notably, DMA
can react with NO2- to form NDMA under the catalysis effect of
formaldehyde, trichloroacetaldehyde, and carbonyl compound
such as acetaldehyde, acetone and trifluoroacetaldehyde
. Bromonitropropanol is the common preservative and
fungicide in cosmetics with the content of 0.04%~0.1%. When
pH is 8~12, Br-, NO2- and formaldehyde could be released from
bromonitropropanol after decomposition, and then catalyzes
their reactions with DMA to form NDMA (Figure 5). Hence, our
law requires that the content of bromonitropropanol should not
Storage process: Generally, the preservatives and stabilizers
are added to cosmetics for the long-term storage and good
performance. The surfactant, viscosifier, pH regulator, emulsifier
and antibacterial preservative with secondary amine can all
catalyze the potential nitrosation reaction at temperatures above
35°C or at acidic pH . In addition, the storage vat with the
nitrite for anti-corrosion and some packaging materials with
residual toxic solvent might result in the nitrosamines formation.
The packaging materials of cosmetics are mainly based on plastic,
and simultaneously, N, N-DMA is widely applied in the packaging
materials due to high thermal stability, low corrosion, and low
toxicity. Thus, the DMA in the plastic containers could volatilize
and shift to the contents, resulting in polluting the cosmetics .
It is greatly difficult to detect the nitrosoamines in cosmetics,
attributed to more types, lower content, greater difference
in the properties of nitrosamines, and possible false positive
disturbance of new nitrosamine formed in the analysis process
. At present, the frequently-used detection methods
include gas chromatography (GC), liquid chromatography
(LC), gas chromatography-mass spectrography (GC-MS), UVVIS
spectrophotometry, thin layer chromatography, micellar
electrokinetic capillary chromatography (MECC), polarography,
surface-enhanced Raman scattering method (SERS), etc.
Furthermore, for the detection of volatile nitrosamines in water
substrate, nitrogen phosphorous detection (NPD) and nitrogen
chemiluminescence detection (NCD) methods are used as the mass spectra (MS) for cost reduction.
GC is a chromatographic separation and analysis method
using gas as mobile phase, suitable for qualitative and quantitative
analysis for volatile organic compounds. In principle, the gas
sample is brought to the chromatographic column by carrier gas.
The forces between stationary phase and sample components
in column are different, so the components can be separated
from each other due to their different outflow time from
column. Similarly, the LC takes liquid as the mobile phase, and
the components in mixture are separated in dependence on the
difference in the affinity of each component for two phases. This
method is characterized by high efficiency, high sensitivity, and
As can be seen by comparison, the GC-MS has not only
the separation capability of GC but also the highly sensitive
identification capability of MS. GC-MS/MS is used to detect 14
nitrosamines in 44 types of drugs such as sartan and ranitidine.
Compared with HPLC, LC-MS has a higher column efficiency and
separation speed, withstands higher column pressure and faster
flow rate. Thus, LC-MS has the higher peak capacity and separation
effect. Small volatile nitrosamines such as NPMA has been
detected in active pharmaceutical ingredient (API) by Vogel et al.
 using LC-MS/MS (Figure 6). (b) Ion chromatograms of all the
nitrosamines detected after adding 50 ng/ml aqueous reference
solution. (c) Ion chromatograms of quantitative nitrosamines
extracted with their own LOD value.
The thermal analysis technology (TEA) is usually used with
GC or LC together. The nitrosamines mixture is firstly separated,
and then the N-NO bond breaks after through the TEA cracking
chamber. The released nitroso (NO) is oxidized by ozone to
electronically excited NO2. Accordingly, the decayed radiation
intensity is in proportion to the concentration of NO . Because
of some advantages such as high sensitivity, high precision
and rapid detection, so this method has been widely applied in
many fields. The methods mentioned above can qualitatively
and quantitatively detect the unknown samples, but they still
have some disadvantages of tedious preprocessing process, high
detection cost, long detection period, expensive instruments, etc.
In recent years, Luo et al. used Raman spectra detection based
on the surface enhanced Raman scattering (SERS) of precious
metals to detect the trace nitrite ions in aqueous solution of
nitrosation (Figure 7). This technology can make the signal intensity
increase by 108~1012 times, and effectively improve the sensitivity
of traditional Raman detection in trace analysis. Moreover, it has
advantages such as ease of operation, strong selectivity, freedom
from interference of water molecules, and fingerprint spectrum,
so with a better detection effect for illegal additives in cosmetics,
i.e., nitrosoamines, Rhodamine B, hydroquinone, and crystal
violet. Representative detection methods of nitrosamine are listed
in Table 2.
Furthermore, there has been a difficulty in directly analyzing
the target due to more types of cosmetics and complex components.
It is necessary to select an appropriate pretreatment method
according to the target to be quantified. The target should be
detected after the enrichment of purified samples. At present, the
pretreatment technologies of common cosmetic samples include
the digestion method, liquid-liquid extraction method, solid phase
extraction method, microextraction techonology, microwaveassisted
extraction method, ultrasonic-assisted extraction
method, etc.  added cerium dioxide into porous silicon
dioxide (SBA-15). The nitrosoamines are extracted from cosmetic
samples with solid-phase microextraction, and meanwhile, the
stirring rod is used to improve the adsorption efficiency. This
solid-phase microextraction-GC-MS method is very sensitive
and efficient in the detection of trace nitrosamines in cosmetics
with the stirring rod support base on Ce-SBA-15 development.
Miralles et al.  detected seven kinds of trace prohibited
N-nitrosoamines in cosmetics using reversed phase dispersionliquid-
phase microextraction-LC. Accordingly, the results show
that the enrichment factor is up to 65, detection limit is 1.8～50
ng/g, with a better repeatability (RSD < 9.8%). More importantly,
this method is used to detect different samples of cosmetics, and
then obtaining the equal relative recovery (80~113%).
The GB/T 29669-2013 published in 2014 stipulates the
detection methods, detection limits and quantitative limits of ten
types of nitrosamines such as NDMA in cosmetics. The industry
development, technology progress and cosmetics supervision
demand prompt the State Food and Drug Administration to
revise the Cosmetic Safety Code, and then the cosmetic safety
technical specification (2015) was put forward. A total of 944
kinds of nitrosamines are listed in the prohibited substances
table, such as N-nitroso dimethylamine, N-nitroso dipropylamine,
and N-Nitrosodiethanolamine. In addition, the standards of the
nitrosamines contents in cosmetics are introduced at abroad. For
example, the International Organization for Standardization has
issued the detection and analysis method for NDELA in cosmetics
and proposed the Technical Guide Document. British Standards
Institution has published the standard detection method of
NDELA in cosmetics. Likewise, France has issued the standard
determination method of NDELA in cosmetics. Table 3 lists the
norms and standards related to nitrosamines in cosmetics.
With constant improvement of cosmetics performance,
their components are more and more complex. Because of longterm
contact with skin, the strongly carcinogenic substance
in cosmetics such as nitrosoamines could result in greatly
potential hazard to the human body. Although some nitrosamine compounds are prohibited in cosmetics in national standards, their coverage and completeness can’t meet the safety supervision
demand of cosmetics. Moreover, the nitrosamines detection
could be interfered by matrix components of cosmetics, and the
existing detection means are insufficient. Therefore, more effort
should be devoted to establishing rapid, large-scale, sensitive,
accurate and low-cost detection methods for nitrosamines, as
well as improving relevant standards and specifications in future.
Simultaneously, much attention to the cosmetics’ safety and
intensification of industrial supervision would make the studies
on nitrosamines contamination in cosmetics develop toward the
norms of cosmetics.
We would like to acknowledge the financial support from
NMPA Key Laboratory of Cosmetic Safety Assessment, Guangdong
Institute for Drug Control (KF2021014); Key Laboratory
of Technological Innovation of Gungdong Medical Products
Administration (2021ZDZ03); Key Laboratory of Green Cleaning
Technology & Detergent of Zhejiang Province (Q202204),
China Postdoctoral Science Foundation (2021M690068), and
Central University Basic Research Fund of China (JUSRP221018,
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