Compendium of the most significant studies with reference to properties, intake, effects.

Soni MG, Taylor SL, Greenberg NA, Burdock GA. Evaluation of the health aspects of methyl paraben: a review of the published literature. Food Chem Toxicol. 2002 Oct;40(10):1335-73. doi: 10.1016/s0278-6915(02)00107-2. 

Abstract. Methyl paraben (CAS No. 99-76-3) is a methyl ester of p-hydroxybenzoic acid. It is a stable, non-volatile compound used as an antimicrobial preservative in foods, drugs and cosmetics for over 50 years. Methyl paraben is readily and completely absorbed through the skin and from the gastrointestinal tract. It is hydrolyzed to p-hydroxybenzoic acid, conjugated, and the conjugates are rapidly excreted in the urine. There is no evidence of accumulation. Acute toxicity studies in animals indicate that methyl paraben is practically non-toxic by both oral and parenteral routes. In a population with normal skin, methyl paraben is practically non-irritating and non-sensitizing. In chronic administration studies, no-observed-effect levels (NOEL) as high as 1050 mg/kg have been reported and a no-observed-adverse-effect level (NOAEL) in the rat of 5700 mg/kg is posited. Methyl paraben is not carcinogenic or mutagenic. It is not teratogenic or embryotoxic and is negative in the uterotrophic assay. The mechanism of cytotoxic action of parabens may be linked to mitochondrial failure dependent on induction of membrane permeability transition accompanied by the mitochondrial depolarization and depletion of cellular ATP through uncoupling of oxidative phosphorylation. Parabens are reported to cause contact dermatitis reactions in some individuals on cutaneous exposure. Parabens have been implicated in numerous cases of contact sensitivity associated with cutaneous exposure; however, the mechanism of this sensitivity is unknown. Sensitization has occurred when medications containing parabens have been applied to damaged or broken skin. Allergic reactions to ingested parabens have been reported, although rigorous evidence of the allergenicity of ingested paraben is lacking.

Matwiejczuk N, Galicka A, Zaręba I, Brzóska MM. The Protective Effect of Rosmarinic Acid Against Unfavorable Influence of Methylparaben and Propylparaben on Collagen in Human Skin Fibroblasts. Nutrients. 2020 May 1;12(5):1282. doi: 10.3390/nu12051282. 

Abstract. Parabens, which are widely used in food, medicines and cosmetics, have a harmful effect on human health. People are most exposed to parabens transdermally by using cosmetic products containing these preservatives. The purpose of this study was to estimate the influence of parabens (methylparaben-MP and propylparaben-PP) on the metabolism of collagen in the human skin fibroblasts and above all, to assess whether rosmarinic acid (RA-50, 100, or 150 M) can protect these cells from the adverse effects of parabens (0.001% MP and 0.0003% PP, 0.003% MP and 0.001% PP, and 0.01% MP and 0.003% PP). The possible mechanisms of RA action were estimated as well. Parabens decreased the expression of collagen type I and III at mRNA and protein levels, while RA (depending on the concentration) provided partial or total protection against these changes. The effective protection against the adverse effects of parabens on cell viability and proliferation was also provided by RA. The beneficial impact of RA on collagen and the fibroblasts resulted from an independent action of this compound and its interaction with parabens. This study allows us to conclude that this polyphenolic compound may protect from unfavorable health outcomes caused by lifetime human exposure to parabens contained in cosmetic products.

Tani H, Takeshita JI, Aoki H, Nakamura K, Abe R, Toyoda A, Endo Y, Miyamoto S, Gamo M, Torimura M, Sato H. Effect of methyl p-hydroxybenzoate on the culture of mammalian cell. Drug Discov Ther. 2017;11(5):276-280. doi: 10.5582/ddt.2017.01054.

Abstract. Several chemicals, such as methyl p-hydroxybenzoate (MHB), have been widely used as preservatives in the water baths of CO2 incubators used for mammalian cell culture, and they are not considered to produce any biological effects. However, no detailed analyses of the effects of these compounds on cultured cells have been reported. In this study, we thus examined whether MHB in the incubator water bath affects cell viability or genome-wide gene expression in mouse embryonic stem cells under control conditions [using only dimethyl sulfoxide (DMSO) in the culture medium] and under chemical-treated conditions using benzene and chloroform; conditions that simulate a cell-based toxicity assay. We found that (i) MHB significantly altered cell growth rate, and (ii) MHB affected gene expression levels related to pathways that modulate cell growth and basic molecular processes, not only under control conditions but also the chemical-treated conditions. Furthermore, Gene Ontology term analyses revealed that the effects of MHB cannot be accounted for by subtracting the gene expression pattern in the control conditions from that in the chemical-treated conditions. Thus, we suggest that the use of MHB or other preservatives in a CO2 incubator water bath is reconsidered in terms of potential confounding effects on cultured cells.

Ishiwata H, Takeda Y, Yamada T, Watanabe Y, Hosagai T, Ito S, Sakurai H, Aoki G, Ushiama N. Determination and confirmation of methyl p-hydroxybenzoate in royal jelly and other foods produced by the honey bee. Food Addit Contam. 1995 Mar-Apr;12(2):281-5. doi: 10.1080/02652039509374302.

Abstract. Methyl p-hydroxybenzoate (methyl paraben) in foods produced by the Honey Bee was determined by HPLC and confirmed by GC-MS. The compound was detected at a mean concentration of 22.3 +/- 6.8 mg/kg (between 14.2 and 31.9 mg/kg) in commercial royal jelly, but was not detected in honey, propolis or pollen lumps at the detection limit of 1 mg/kg. Fresh royal jelly collected from apiaries contained methyl p-hydroxybenzoate at a concentration of 20.3 +/- 4.7 mg/kg (between 12.5 and 31.7 mg/kg). These results indicate that the methyl p-hydroxybenzoate in royal jelly is not added but is a natural component.

Darbre PD, Harvey PW. Parabens can enable hallmarks and characteristics of cancer in human breast epithelial cells: a review of the literature with reference to new exposure data and regulatory status. J Appl Toxicol. 2014 Sep;34(9):925-38. doi: 10.1002/jat.3027.

Abstract. A framework for understanding the complexity of cancer development was established by Hanahan and Weinberg in their definition of the hallmarks of cancer. In this review, we consider the evidence that parabens can enable development in human breast epithelial cells of four of six of the basic hallmarks, one of two of the emerging hallmarks and one of two of the enabling characteristics. In Hallmark 1, parabens have been measured as present in 99% of human breast tissue samples, possess oestrogenic activity and can stimulate sustained proliferation of human breast cancer cells at concentrations measurable in the breast. In Hallmark 2, parabens can inhibit the suppression of breast cancer cell growth by hydroxytamoxifen, and through binding to the oestrogen-related receptor gamma may prevent its deactivation by growth inhibitors. In Hallmark 3, in the 10 nm-1 μm range, parabens give a dose-dependent evasion of apoptosis in high-risk donor breast epithelial cells. In Hallmark 4, long-term exposure (>20 weeks) to parabens leads to increased migratory and invasive activity in human breast cancer cells, properties that are linked to the metastatic process. As an emerging hallmark methylparaben has been shown in human breast epithelial cells to increase mTOR, a key regulator of energy metabolism. As an enabling characteristic parabens can cause DNA damage at high concentrations in the short term but more work is needed to investigate long-term, low-dose mixtures. The ability of parabens to enable multiple cancer hallmarks in human breast epithelial cells provides grounds for regulatory review of the implications of the presence of parabens in human breast tissue.

Jian L, Li Wan Po A. Ciliotoxicity of methyl- and propyl-p-hydroxybenzoates: a dose-response and surface-response study. J Pharm Pharmacol. 1993 Oct;45(10):925-7. doi: 10.1111/j.2042-7158.1993.tb05624.x. 

Abstract. The effect of methyl-p-hydroxybenzoate (methyl paraben, MHB) and propyl-p-hydroxybenzoate (propyl paraben, PHB) on ciliary beat frequency was investigated using surface-response methodology. Both compounds are shown to be ciliotoxic at concentrations equal to or lower than those in use for preserving aqueous formulations. The dose-response curves show the typical sigmoidal pattern. Interaction by the two compounds is evidenced by the curved response surface for ciliotoxicity.

Cacua-Ortiz SM, Aguirre NJ, Peñuela GA. Methyl Paraben and Carbamazepine in Water and Striped Catfish (Pseudoplatystoma magdaleniatum) in the Cauca and Magdalena Rivers. Bull Environ Contam Toxicol. 2020 Dec;105(6):819-826. doi: 10.1007/s00128-020-03028-z. 

Abstract. Between 2017 and 2019, samplings were carried out in the San Jorge, Cauca and Magdalena River basins in Colombia, to determine the presence of methyl paraben and carbamazepine in water and Pseudoplatystoma magdaleniatum. For the analysis of the samples, a validation of the analytical method was performed, following the EPA method 1694 (Pharmaceutical and personal care products in water), with slight modifications. This was done by liquid-chromatography tandem mass spectrometry, for quantification of methyl paraben and carbamazepine, including parameters of linearity, accuracy precision and veracity. Carbamazepine was found in the Magdalena River at 8.03 ± 0.01 µg/L in transition season. In fish samples, methyl paraben and carbamazepine were detected in a range between 32 and 90.80 µg/kg in transition and dry seasons.

Ishiwatari S, Suzuki T, Hitomi T, Yoshino T, Matsukuma S, Tsuji T. Effects of methyl paraben on skin keratinocytes. J Appl Toxicol. 2007 Jan-Feb;27(1):1-9. doi: 10.1002/jat.1176. 

Abstract. Some ingredients of dermatological formulations result in skin irritation and allergy. In particular, preservatives have been reported extensively as a cause of allergic contact dermatitis. The study focused on parabens which have been used extensively as antimicrobial preservatives in foods, drugs and cosmetics. The aim of this study was to clarify the effects of the daily use of methyl paraben (MP) on human skin. The concentrations of MP in the stratum corneum (SC) of the human forearm were measured using the cup method and GC-MS after daily applications of MP containing formulations. The study also investigated the effects of long-term exposure to MP on keratinocytes in vitro. Normal human keratinocytes and the skin equivalents were cultured in the medium containing MP. The following changes were analysed: proliferating ability, apoptotic cells, morphological changes, mRNA and protein expressions. After 1 month of daily applications of MP containing formulations, MP remained unmetabolized and persisted slightly in the SC. MP decreased the proliferating ability of keratinocytes and changed the cell morphology. MP also decreased the expressions of hyaluronan synthase 1 and 2 mRNAs and type IV collagen. In contrast, it increased the expressions of involucrin and HSP27. Furthermore, MP influenced the epidermal differentiation of the skin equivalent. These results suggest that MP exposure through application of dermatological formulations results in MP persistence and accumulation in the SC, and that MP might influence the aging and differentiation of keratinocytes.

Cha HJ, Bae S, Kim K, Kwon SB, An IS, Ahn KJ, Ryu J, Kim HS, Ye SK, Kim BH, An S. Overdosage of methylparaben induces cellular senescence in vitro and in vivo. J Invest Dermatol. 2015 Feb;135(2):609-612. doi: 10.1038/jid.2014.405.

Abstract. Methylparaben (MP) is used to extend the shelf-life of industrial chemicals (Cashman and Warshaw, 2005). However, when the skin is exposed to MP, this compound permeates the epidermis and the dermis and particularly shows higher permeation compared with other parabens because of difference in their lipophilicity (El Hussein et al., 2007). It exhibits various adverse dermatological responses, such as allergic reaction, synergistic cytotoxic effect of UV radiation, and breast cancer development (Nardelli et al., 2009, Dagher et al., 2012). Concentrations of MP exceeding 4 mg ml  1 in industrial products are known to be harmful (Darbre and Harvey, 2008; CIR expert panel, 2008). Although MP persists in the dermis (El Hussein et al., 2007), little is known about its side-effects ormolecular mechanism in the dermis.

Methyl p-hydroxybenzoate (Methylparaben) is a 4-hydroxybenzoate ester of p-hydroxybenzoic acid.

The name defines the structure of the molecule

• "Methyl" indicates the presence of a methyl group, which is an alkyl group with the formula CH₃.
• "p-hydroxy" indicates the presence of a hydroxy group (OH) in the para position relative to the benzoate functional group on the benzene structure.
• "Benzoate" indicates the presence of a benzoate group, which is an ester of benzoic acid.

Description of raw materials used in production

• p-Hydroxybenzoic Acid - An aromatic compound that is the primary precursor of methylparaben.
• Methanol - Used as an alkylating agent to esterify the p-hydroxybenzoic acid.
• Catalyst - For example, sulfuric acid, which accelerates the esterification reaction.

Step-by-step summary of industrial chemical synthesis process.

• Mixing - The p-hydroxybenzoic acid and methanol are mixed together.
• Esterification - The mixture is heated in the presence of a catalyst to form the methyl ester of p-hydroxybenzoic acid.
• Cooling and Separation - The reacted mixture is cooled and the formed product separates.
• Purification - The crude product is purified through techniques such as distillation or crystallization.
• Drying - Moisture is removed from the product.
• Packaging - Methyl p-hydroxybenzoate is packaged in suitable containers for transport and sale.
• Quality Control - The final product undergoes various quality checks to ensure it meets specifications.

Appears in the form of a white powder. Stable. Incompatible with strong bases and strong oxidising agents.

What it is used for and where

Food

Preservative. It is labelled with the number E218 in the list of European food additives as a preservative. Although this allergen is being used less and less, warning should be given because it is labelled under different nomenclature, with different names corresponding to its many synonyms.

Cosmetics

A preservative belonging to the paraben family, a class of chemical compounds to which the scientific literature attributes endocrine disrupting characteristics. Although this allergen is less and less used, warning must be given because it is written on labels under different nomenclature, with different names corresponding to its many synonyms.

Preservative additive used in various industries and serves to fight bacteria, fungi, yeasts and moulds. Like all esters and salts of the Paraben class, it is also often found in cosmetic, pharmaceutical and food formulations.

It is listed with the number E218 in the European food additives list as a preservative.

Methylparaben (MP) is used to extend the shelf life of industrial chemicals (Cashman and Warshaw, 2005). However, when the skin is exposed to MP, this compound permeates the epidermis and dermis and shows in particular greater permeation than other parabens due to the difference in their lipophilicity ( El Hussein et al., 2007 ). It exhibits several adverse dermatological reactions, such as allergic reaction, the cytotoxic synergistic effect of UV radiation and the development of breast cancer ( Nardelli et al., 2009 , Dagher et al., 2012 ). MP concentrations above 4 mg ml -1 in industrial products are known to be harmful ( Darbre and Harvey, 2008; CIR Expert Group, 2008 ). Although MP persists in the dermis ( El Hussein et al., 2007 ), little is known about its side effects or molecular mechanism in the dermis.

Overall, the results show that MP induces cellular senescence in vitro and in vivo, via the GR-c-Jun-ROS pathway, and MP-induced cellular senescence alters ECM components. Although the treatment doses of MP used in this study seem high compared to the limit of industrial use (CIR Expert Group, 2008), the data provide evidence for the hypothesis that MP overdose may induce alterations in ECM components by concentrating senescent fibroblasts in the dermis (1).

Methylparaben is, like all parabens, a debated component about whose safety many doubts have been raised, in particular because of the damage it would cause to the aquatic environment where it is discharged after use (2).

Exposure to methylparaben has been associated with adverse health outcomes and exposure to ultraviolet rays may amplify its toxicity (3).

To reduce the toxicity of parabens in the aquatic environment, a system called the Fenton process is applied (4).

Clinical studies have suggested that Methylparaben increases breast cancer proliferation and may play a direct role in chemoresistance by modulating stem cell activity (5).

Parabens, but in particular Methylparaben, promotes adipogenesis but suppresses the serum marker of bone formation in vivo and indicates possible negative health consequences (6) and may therefore contribute to obesity (7) furthermore, exposure to parabens is associated with DNA damage, male infertility and endocrine disruption in adults (8).

To counteract and mitigate the negative effects of methylparaben on human health, this study suggests that a polyphenolic compound, rosmarinic acid, may protect against unfavourable health outcomes caused by lifelong human exposure to parabens in cosmetic products (9).

The most relevant studies and their abstracts have been selected to explore this in more depth:

     Methylparaben studies

Typical commercial product characteristics Methylparaben 

Appearance	White crystalline powder
Boiling Point	265.5±13.0°C at 760 mmHg
Melting Point	125-128°C
Flash Point	116.4±12.6°C      280°C
Density	1.2±0.1 g/cm3
Vapor Pressure	0.0±0.6 mmHg at 25°C
Refraction Index	1.547
PSA	46.53000
LogP	1.87
Loss on drying	0.5% max
Acidity	0.1mg/g max
Sulphate Ash	0.1% max
Heavy Metal	10ppm max
Chemical Safety

Price

$2.10 - $10.40/ kg

• Molecular Formula    C₈H₈O₃
• Linear Formula    HOC₆H₄CO₂CH₃
• Molecular Weight  152.15
• CAS   99-76-3 
• UNII    A2I8C7HI9T
• EC Number   202-785-7
• DSSTox Substance ID  DTXSID4022529
• IUPAC  methyl 4-hydroxybenzoate
• InChl=1S/C8H8O3/c1-11-8(10)6-2-4-7(9)5-3-6/h2-5,9H,1H3
• InChl Key      LXCFILQKKLGQFO-UHFFFAOYSA-N
• SMILES   COC(=O)C1=CC=C(C=C1)O
• MDL number  MFCD00002352
• PubChem Substance ID    329815219
• ChEBI  31835
• RTECS  DH2450000
• Beilstein    509801
• FEMA    2710
• RXCUI    29903   
• NSC      406127    3827
• NACRES NA.25 

Synonyms :

• E218
• Sodium Methylparaben
• Methylparaben
• Solparol
• Metilparaidrossibenzoato

• Methyl-4-hydroxybenzoate
• p-Hydroxybenzoic acid methyl ester
• methyl para-hydroxybenzoate
• Metagin
• NIPAGIN
• p-Hydroxybenzoic acid, methyl ester
• p-Hydroxybenzoic methyl ester
• Methyl parasept
• Tegosept M
• 4-Hydroxybenzoic acid methylester
• 4-Hydroxybenzoic Acid Methyl Ester
• 4-(Methoxycarbonyl)phenol
• Methyl parahydroxybenzoate

References_________________________________________________________________________

(1)  Cha HJ, Bae S, Kim K, Kwon SB, An IS, Ahn KJ, Ryu J, Kim HS, Ye SK, Kim BH, An S. Overdosage of methylparaben induces cellular senescence in vitro and in vivo. J Invest Dermatol. 2015 Feb;135(2):609-612. doi: 10.1038/jid.2014.405.

(2) Terasaki M, Abe R, Makino M, Tatarazako N. Chronic toxicity of parabens and their chlorinated by-products in Ceriodaphnia dubia. Environ Toxicol. 2015 May-Jun;30(6):664-73. doi: 10.1002/tox.21944. 

Popa DS, Bolfa P, Kiss B, Vlase L, Păltinean R, Pop A, Cătoi C, Crişan G, Loghin F. Influence of Genista tinctoria L. or methylparaben on subchronic toxicity of bisphenol A in rats. Biomed Environ Sci. 2014 Feb;27(2):85-96. doi: 10.3967/bes2014.021. 

(3) Lee J, Park N, Kho Y, Lee K, Ji K. Phototoxicity and chronic toxicity of methyl paraben and 1,2-hexanediol in Daphnia magna. Ecotoxicology. 2017 Jan;26(1):81-89. doi: 10.1007/s10646-016-1743-6. 

(4) Martins RC, Gmurek M, Rossi AF, Corceiro V, Costa R, Quinta-Ferreira ME, Ledakowicz S, Quinta-Ferreira RM. Application of Fenton oxidation to reduce the toxicity of mixed parabens. Water Sci Technol. 2016 Oct;74(8):1867-1875. doi: 10.2166/wst.2016.374.

(5) Lillo MA, Nichols C, Perry C, Runke S, Krutilina R, Seagroves TN, Miranda-Carboni GA, Krum SA. Methylparaben stimulates tumor initiating cells in ER+ breast cancer models. J Appl Toxicol. 2017 Apr;37(4):417-425. doi: 10.1002/jat.3374.

(6) Hu P, Kennedy RC, Chen X, Zhang J, Shen CL, Chen J, Zhao L. Differential effects on adiposity and serum marker of bone formation by post-weaning exposure to methylparaben and butylparaben. Environ Sci Pollut Res Int. 2016 Nov;23(21):21957-21968. doi: 10.1007/s11356-016-7452-0.

(7) Hu P, Chen X, Whitener RJ, Boder ET, Jones JO, Porollo A, Chen J, Zhao L. Effects of parabens on adipocyte differentiation. Toxicol Sci. 2013 Jan;131(1):56-70. doi: 10.1093/toxsci/kfs262.

(8) Baker BH, Wu H, Laue HE, Boivin A, Gillet V, Langlois MF, Bellenger JP, Baccarelli AA, Takser L. Methylparaben in meconium and risk of maternal thyroid dysfunction, adverse birth outcomes, and Attention-Deficit Hyperactivity Disorder (ADHD). Environ Int. 2020 Jun;139:105716. doi: 10.1016/j.envint.2020.105716.

(9) Matwiejczuk N, Galicka A, Zaręba I, Brzóska MM. The Protective Effect of Rosmarinic Acid Against Unfavorable Influence of Methylparaben and Propylparaben on Collagen in Human Skin Fibroblasts. Nutrients. 2020 May 1;12(5):1282. doi: 10.3390/nu12051282.