With not much imagination, phthalic acid has been so called because it looks like naphthalene (Figure 1). With two carboxyl groups, phthalic acid is prone to chemical modifications and can yield, for instance, phthalate esters. When the esters obtained by adding one or two alkyl groups are mixed with polyvinyl and heated, they disrupt the polyvinyl network and allow the resulting material to acquire flexibility. That is to say that, when added to plastics, phthalates allow the long polyvinyl molecules to slide against one another and lose their inherent stiffness. They are, therefore, called “plasticizers” and are used in many industrial applications.

Things like shower curtains, boots and IV tubes are made from that same hard white plastic that a plumber would use, but when 30% by weight of a specific phthalate is added, one obtains soft pliable vinyl plastic. Phthalates are likely to be used in many hundreds if not thousands of different products. Since they do not form covalent bonds with polyvinyl, they can be released in the environment. Therefore, their safety must be assessed.

If we take the simplest of polycyclic aromatic hydrocarbon, naphthalene (below),

and make sone chemical hocus-pocus on its right-hand side, we obtain phthalic acid as shown here:















Phthalates are also used in many personal care products such as colognes, perfumes, soaps and shampoos.

Phthalates in Cosmetics

The first phthalates used in cosmetic products have been dibutylphthalate (DBP), dimethylphthalate (DMP) and diethylphthalate (DEP). DBP was used as a plasticizer in nail polishes, making them less brittle to reduce cracking; DMP was used in hair sprays to allow the formation of a flexible film on the hair. DEP was used as a solvent and fixative in fragrances.

Photo-chemists know that polycyclic aromatic hydrocarbons absorb far-ultraviolet radiation (UVC) and that when they are modified by adding alkyl groups, their absorption maximum undergoes a redshift and can end up in the UVB or even in the UVA. It is therefore not surprising to learn that in the quest for photostable UVA filters, some phthalates were investigated. The most successful result from this quest is represented by terephthalylidenedicamphor sulfonic acid (TPDC-SA) also known under the USAN name Ecamsule or the tradename Mexoryl SX. When exposed to ultraviolet radiation, Ecamsule undergoes reversible photoisomerization, followed by photoexcitation. The absorbed energy is then released as thermal energy, and the absorbed UV photon does not penetrate the skin.

However, the chance that the absorbed energy be transferred to the surrounding molecular oxygen with the consequent formation of the devastating singlet oxygen is quite high: the quantum yield for this to occur is about 9%.1 This means substantially that one in ten photons generates singlet oxygen. When this happens on the skin where sunscreens are generally applied, singlet oxygen can create havoc by triggering the peroxidative cascade in cell membranes as well as cytoskeleton damage and DNA oxidation.

Safety of Phthalates

Phthalates are widely used in plastics and may be released from plastics. Many toys are made with plastics and young children tend to chew on toys. As a result, more consumers want to know what products contain phthalates and what are the safety issues associated with phthalates. Consumers can tell whether some products contain phthalates by reading ingredient labels. Exposure to phthalates can damage the liver, kidneys and lungs, as well as the reproductive system.

Purposedly exposing human being to possibly toxic materials is unethical and many toxicological studies are performed using laboratory models. Rats fed for 15 weeks with 160mg/kg/d of phthalates underwent a 25% loss of serum testosterone relative to their status at the beginning of the experiment. A dose of 160mg/kg/d means that laboratory rats (weighing about 300 grams) were fed 50mg of phthalates every day for 15 weeks.²

The uptake of one phthalate (di-n-butyl-phthalate) by human beings has been estimated by several scientific agencies such as the UK Ministry of Agriculture, Fisheries and Food; Health Canada; the US Agency of Toxic Substances and Diseases Registry; and the International Program on Chemical Safety. The result from Health Canada is that the overall uptake of di-n-butyl phthalate from ambient and indoor air, drinking water and food is about 5 micrograms per kg bodyweight per day in children below 4 years of age, and about 2 micrograms per kg bodyweight per day in adults above the age of 20.

The results from the different agencies disagree, so that the maximum estimate for total intake is about 7 microgram per kg body weight per day in adults, and the minimum estimate is 0.01 microgram per kg body weight per day. Irrespective of the discrepancies, these numbers are quite smaller than the phthalate uptake in the experiments performed with laboratory rats already described, and yet they justify concern about possible nefarious effects in human beings.

The Consumer Product Safety Commission (CPSC) announced the permanent prohibition of children’s toys and childcare products that contain more than 0.1% by weight of phthalates. The FDA also limits the use of phthalates in certain consumer products, such as food contact materials. The National Institute for Occupational Safety and Health recommended airborne exposure limit (REL) to 5 mg/m3 averaged over a 10-hour work-shift.

As far as phthalates in cosmetics are concerned, their uptake from cosmetic products and fragrances has been estimated and reported in a 2004 scientific paper.⁴ The abstract of this paper summarizes the situation (the “bolding” of the characters is mine):

“Di-Butyl-Phthalate (DBP) was detected in 19 of the 21 nail polishes and in 11 of the 42 perfumes, and Di-Ethyl-Phtalate (DEP) was detected in 24 of the 42 perfumes and 2 of the 8 deodorants. Median exposure levels to phthalates in cosmetics by dermal absorption were estimated to be 0.0006 µg/kg body weight (bw)/d for Di-(2-ethylhexyl)-Phthalate (DEHP), 0.6 µg/kg bw/d for DEP, and 0.103 µg/kg bw/d for DBP. Furthermore, if phthalates in cosmetics were assumed to be absorbed exclusively via 100% inhalation, the median daily exposure levels to phthalates in cosmetics were estimated to be 0.026 µg/kg bw/d for DEHP, 81.471 µg/kg bw/d for DEP, and 22.917 µg/kg bw/d for DBP, which are far lower than the regulation levels set buy the Scientific Committee on Toxicity, Ecotoxicity, and the Environment (CSTEE) (37 µg/kg bw/d, DEHP), Agency for Toxic Substances and Disease Registry (ATSDR) (7000 µg/kg bw/d, DEP), and International Programme on Chemical Safety (IPCS) (66 µg/kg bw/d, DBP), respectively.

Based on these data, hazard indices (HI, daily exposure level/regulation level) were calculated to be 0.0007 for DEHP, 0.012 for DEP, and 0.347 for DBP. These data suggest that estimated exposure to phthalates in the cosmetics mentioned are relatively small.”

References

1. Cantrell A, McGarvey DJ & Truscott, G. Photochemical and photophysical properties of sunscreens. In (P.U Giacomoni Ed) Sun Protection in Man. Elsevier, Amsterdam London New York (2001) pages 495-519
2. Hai-Tao Gao et al (2017) Effects of six priority controlled phthalate esters with long-term low-dose integrated exposure on male reproductive toxicity in rats. Food and Chemical Toxicology 101 : 94-104
3. Kavlock R et al (2002) NTP Center for the evaluation of Risks ti Human Reproduction: phthalates expert panel report on the reproductive and developmental toxicity of di-n-butyl phthalate.
4. Hyun Jung Koo & Byung Mu Lee (2004) Estimated Exposure to Phthalates in Cosmetics and Risk Assessment. J Toxicol Environ Health, Part A. 67 : 1901-1914

---

Paolo Giacomoni, PhD
Insight Analysis Consulting
[email protected]
516-769-6904
 
Paolo Giacomoni acts as an independent consultant to the skin care industry. He served as Executive Director of Research at Estée Lauder and was Head of the Department of Biology with L’Oréal. He has built a record of achievements through research on DNA damage and metabolic impairment induced by UV radiation as well as on the positive effects of vitamins and antioxidants. He has authored more than 100 peer-reviewed publications and has more than 20 patents. He is presently Head of R&D with L.RAPHAEL—The science of beauty—Geneva, Switzerland.