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Introduction

Cosmetic products may undergo oxidation, leading to rancid-ity, discoloration, and destabilization. This oxidation process can be minimized by the control of raw materials quality, pres-ervation, and appropriate storage times and conditions. Nev-ertheless, when applied on the skin, the product is exposed to enviro nmental factors as sunlight and oxygen, which can easily and quickly start oxidation and rancidity processes. The rancidity process can be roughly divided into an initiation, a propagation, and a termination step, with different radical species involved in each step. UV radiation can lead to radical chain reactions inside the formulation. Some active ingredients inside the cosmetic formulation might trigger these radical chain reactions or might act as catalyzer:

• Some organic UV-filters;

• Photocatalytically active TiO2 (uncoated)

• Perfume components containing hydroperoxides

• Unsaturated lipids of natural oils

Although these free radicals should not be harmful for the consumers (they will not penetrate into the living lay-ers of the skin), they can lead to a deterioration of the

formulation quality. Furthermore, the presence of hydroxyper-oxides and other peroxide free radicals is known to induce photo-toxic/chemo-toxic skin reactions [1]. Photo allergic dermatitis is affecting 1 to 2 % of the popula-tion. One of the most common form of this UV-induced skin reaction is given by Acne aestivalis (also known as Mallorca acne), a special kind of polymorphous light eruption. It is a monomorphous eruption consisting of multiple, uniform, red, papular lesions, reported to occur after sun exposure. Acne aestivalis is a photo-induced severe skin reaction, be-

High Levels of Free Radicals in Suncare Products Induce Acne Aestivalis in Sensitive SubjectsK. Jung*, U. Heinrich**, H. Tronnier**, M. Schnyder***, B. Herzog***, T. Herrling*

Fig. 1 Case report of Acne aestivalis (Source: Institute Dermatronnier, [4])

abstract

The market segment of suncare products for protection of sensitive skin against photodermatosis is growing. Specifically, pro-tection against Acne aestivalis (“Mallorca-Acne”) is perceived as a strong claim for this product category. There is evidence

that peroxide free radicals, deriving from certain formulation components, are involved in the induction of photo-toxic skin reactions. These UV-induced free radicals can be assessed by an ESR-based method called Radical Potential (RP), by exposing formulations to UV radiation. The aim of this study was to find a correlation between the amount of UV inducible peroxides of sunscreen products and the clinical symptoms of Acne aestivalis. Two sunscreen formulas (SPF 30) containing organic UV-filters only, with an identical protection in the UV B region and a comparable protection in the UV A spectral range, have been pro-duced. For both formulations the amount of UV-inducible free radicals was assessed by the RP (Radical Potential). In addition, both formulas were tested in a clinical study with subjects with a history of Acne aestivalis. Very different RP values (levels of UV-induced free radicals) and completely different skin reactivity have been obtained, where an excellent correlation between the in vitro-parameter (RP) and the clinical symptoms could be shown. To our knowledge these results for the first time provide direct evidence for a strong correlation between UV inducible free radicals of formulations and the potential to induce A. aesti-valis in sensitive subjects. Furthermore it offers a rationale for the development of low risk sunscreen formulations by selection of suitable filter systems combined with in situ ESR analysis.

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longing to the terminus “polymorpheous light dermatosis” (PLD), with immune- and autoimmune co-involvement. It is often correlated to sunscreens, since the affected skin areas are exposed to frequent sun irradiation, especially UV A ra-diation.There is evidence, that peroxide reactions are involved in the pathophysiologic mechanism. Antioxidants have been shown to ameliorate the symptoms, but the entire molecu-lar mechanism is still not understood. [2,3].The aim of the present investigation was to find a correla-tion between the amount of UV-inducible free radicals inside a sunscreen formulation and the clinical symptoms of Acne aestivalis.

RP Method (Radical Potential)

A semistable spin probe PCA (2,2,5,5-tetramethyl pyrrolidine N-oxyl, 0.01 mM final concentration) was added to the di-luted cosmetic product. The samples are inserted in capillary quartz tubes, the concentration of the spin marker is moni-tored by ESR spectroscopy before and after defined UV radia-tion doses. The PCA spin probe is photostable and resistant to antioxidants, but it promptly reacts with the UV generated free radicals inside the samples (mainly hydroxyl radicals, lipid peroxides and lipidic radicals). The amount of UV generated free radicals can be quantitatively detected from a calibra-tion curve and the results are expressed in percentage of UV-inducible free radicals. The UV irradiation of the samples was performed with a UV solar simulator 300 W Oriel (Newport). The irradiances as in-tegrated value over the spectral ranges were E (UVB=280-320) = 23.5 W/m2 and E (UVA=320-400 nm) = 180 W/m2. Increase of UV doses was achieved by increasing irradiation times. The emitting Intensity is controlled before each measurement. A cut-off filter 320 nm (ITOS W-NG-320, Schott) was used to obtain only UV A radiation.ESR measurements were performed with a high sensitive X-band bench top Electron Spin Resonance Spectrometer Mi-niScope MS300, supplied from Magnettech GmbH Berlin, Germany [5].

Clinical Study

The test subjects, all being sensitive to Acne aestivalis, are irradiated using only UV A radiation, on 5 successive days. A Solar Simulator (SOL 5, Hönle AG, Germany) was used. The irradiation dosis was 20 J/cm2, far below the erythema thresh-old. The test formulations, as well as the positive and negative control, are applied 10 minutes prior to the irradiation on the décolleté area. The skin reactions are evaluated directly after each irradiation and again after 24 hours, prior to the next irradiation dosis. A market sunscreen gel (SPF 30) served as a negative control, which has never provoked a skin reaction in sensitive subjects.A sunscreen formulation served as a positive control, which provokes Acne aestivalis in disposed subjects.

Results

An example of RP data is given in Fig. 2. A cosmetic formula-tion was spiked with natural oils or perfume oils (PO). The Almond oil showed higher radical generation compared to Olive oil, probably due to differences in the fatty acid compo-sition and the oxidation grade. The two perfume oils showed

Fig. 2 Example of free radical generation in a cosmetic formulation (placebo) spiked with natural oils or perfume oils (PO)

AD

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very different reactions: PO “A” showed very low radical gen-eration (RP = 6.6 %), whereas PO “B” showed a strong radi-cal generation under UV (RP = 63.9 %). Sensorial properties had not changed. The added perfume oils differ with respect to terpene composition, oxidation state, and especially in the content of hydroperoxide-terpenes, what is most likely the reason for their different behaviours.Two sunscreen formulations have been produced, both hav-ing an SPF of 30 and the same UVA/UVB ratio. The UV-filter composition differed (see Tab. 1). Formulation 12-1 contained only photostable UV-filters, where-as formulation 12-2 contained also photo-unstable filters. The Radical Potential (RP) of both formulations was detected, using the full spectrum UV light (280-400 nm), and the UV A region of the spectrum (320-400 nm) only, since Acne aestivalis is report-ed to be induced mainly by UV A radiation. Formulation 12-1 did not induce free radicals, whereas formulation 12-2 showed a high radical generation, both under full-spectrum UV and UV A radiation (45.3 % and 21.9 %, respectively). (see Tab. 2).

The two sunscreens 12-1 and 12-2 were tested regarding their capacity to induce Acne aestivalis in sensitive subjects:

Positive Control

The most intensive reactions were observed after application of the positive control. This internal standard serves as a con-

Phase INCI 12-1 12-2

A

Sucrose Polystearate (and) Cetyl Palmitate 3.00 3.00

Disodium Cetearyl Sulfosucchinate 1.00 1.00

Cetearyl Alcohol 1.00 1.00

Lauryl Lactate 5.00 5.00

C12-C15 Alkyl Benzoate 10.00 10.00

Dibutyl Adipate 10.00 10.00

Phenoxyethanol (and) Ethylhexylglycerin 1.00 1.00

Ethylhexyl salicylate (EHS) 5.00 5.00

Butyl methoxydibenzoylmethane (BMDBM) 4.00

Diethylhexyl butamido triazone (DBT) 3.00

Bis-ethylhexyloxyphenol methoxyphenyl triazine (BEMT) 2.00 2.00

Ethylhexyl triazone (EHT) 3.00 2.50

Diethylamino Hydroxybenzoyl Hexyl Benzoate (DHHB) 3.00

B

Aqua 44.60 39.10

Glycerine 2.00 2.00

Xanthan Gum 0.20 0.20

Disodium EDTA 0.20 0.20

C

Phenylbenzimidazol sulfonic acid (PBSA) 2.00

Aqua 5.00

Tromethamine 2.00

D Methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT) 3.50

E Undecan, Tridecan 2.00 2.00

Tab. 1 INCI of the two SPF 30 sunscreen formulas

Product % of induced free

radicals UVAB % of induced free

radicals UVA

12-1 0 ± 0,7 0 ± 0,1

12-2 45,3 ± 1.0 21,9 ± 0.2

Tab. 2 Relative amount of free radicals. N = 2

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trol of the inducibility of Acne aestivalis in the selected test persons.

Negative Control

In the test areas treated with the negative control (market sunscreen gel- formulation) no skin reactions were observed in any of the subjects.(Reference for Positive and Negative control: confidential in-formation DermaTronnier)

12-1

In the test areas treated with this sunscreen formula, no skin reactions could be observed dur-ing the 5 days treatment in none of the 6 subjects. This sunscreen formula offered complete protection against Acne aestivalis.

12-2

This test product provoked skin re-actions classified to Acne aestivalis in 5 out of 6 subjects. Subject n°4 showed only slight symptoms, which occurred already after the third ex-position day. Subjects n° 1, 5, and 6 showed light to distinct reaction dur-ing the exposition time, so that after the third and fourth day no further ir-radiation and treatment could be ap-plied for ethical reasons. Subject n° 3 showed already severe skin reactions after the second treatment day, so that no further irradiation could be applied after day 4.

The results in Tab. 3 were quantified using a score system, which is illustrat-ed in Fig. 3

Discussion

Two sunscreen formulas (SPF 30) have been under investigation. Although both contained organic UV-filters only and provide a comparable protection in the UV A spectral range, very dif-ferent RP values (levels of UV-induced free radicals) and completely different skin reactivity have been obtained. An excellent correlation between the in vitro-parameter (RP) and the clinical symptoms could be shown.

Score value:0 = no reaction 0± = light reaction 1+ = distinct reaction 2++ = severe reaction 3+++ = very severe reaction 4n.t. = no treatment

Test product Observation time P1 P2 P3 P4 P5 P6UV14-132-12-1 Beobachtungszeit 0 0 0 0 0 0

1. Day before irradiation 0 0 0 0 0 0

1. Day after irradiation 0 0 0 0 0 0

2. Day before irradiation 0 0 0 0 0 0

2. Day after irradiation 0 0 0 0 0 0

3. Day before irradiation 0 0 0 0 0 0

3. Day after irradiation 0 0 0 0 0 0

4. Day before irradiation 0 0 0 0 0 0

4. Day after irradiation 0 0 0 0 0 0

5. Day before irradiation 0 0 0 0 0 0

UV14-132-12-2 5. Day after irradiation 0 0 0 0 0 0

1. Day before irradiation 0 0 0 0 0 0

1. Day after irradiation 0 0 0 0 0 0

2. Day before irradiation 0 0 ± 0 0 0

2. Day after irradiation 0 0 ± ± 0 0

3. Day before irradiation ± 0 ± ± 0 ±

3. Day after irradiation ± 0 ++ n.t. ± 0 + n.t.

4. Day before irradiation + 0 ++ ± ± +

4. Day after irradiation + n.t. 0 ++ n.t. ± + n.t. + n.t.

5. Day before irradiation + 0 ++ ± + +

Negative control 5. Day after irradiation 0 0 0 0 0 0

1. Day before irradiation 0 0 0 0 0 0

1. Day after irradiation 0 0 0 0 0 0

2. Day before irradiation 0 0 0 0 0 0

2. Day after irradiation 0 0 0 0 0 0

3. Day before irradiation 0 0 0 0 0 0

3. Day after irradiation 0 0 0 0 0 0

4. Day before irradiation 0 0 0 0 0 0

4. Day after irradiation 0 0 0 0 0 0

5. Day before irradiation 0 0 0 0 0 0

Positive control 5. Day after irradiation 0 0 0 0 0 0

1. Day before irradiation ± 0 0 0 0 0

1. Day after irradiation 0 0 ± 0 0 0

2. Day before irradiation ± 0 ± 0 0 0

2. Day after irradiation + n.t. 0 + n.t. ± ± ±

3. Day before irradiation + ± + ± ± +

3. Day after irradiation + n.t. ± + n.t. ± ± + n.t

4. Day before irradiation + ± + + + +

4. Day after irradiation + n.t. + n.t. + n.t. + n.t. + n.t. + n.t.

5. Day before irradiation + + + + + +

Tab. 3 Evaluation of the adverse skin reaction of treated subjects where 24 is the sum of the highest possible skin reaction (score value 4 x 6 subjects)

Fig. 3 Score evaluation of the clinical study

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Despite the relatively low number of subjects, this result pro-vides an excellent correlation between the in vitro-parameter (RP) and the clinical symptoms, corroborating the hypothesis of involvement of free radical species in Acne aestivalis.With an RP value of 0, test formula 12-1 had no UV inducible free radical potential, whereas 12-2 had a high one, with RP values of 45.3 % in the UVB/A range and 21.9 % under pure UVA irradiation. In parallel, the low free radical potential 12-1 formula did not elicit Acne aestivalis symptoms in the clinical study, in contrast to 12-2, with a very high incidence rate of 5 out of 6 subjects.The differences in the two formulas only lay in different UV-filter combination. Formula 12-1 contained highly stable or-ganic, oil soluble or particulate UV-filters, whereas formula 12-2 contained in addition non-stabilized BMDBM and water-soluble PBSA. The first one is known to undergo photoreac-tions under UV radiation leading to intermediate radical spe-cies [6]; the second one converts into an organic semistable free radicals under UV radiation [7].In the present study Acne aestivalis has been provoked by a formulation containing high levels of UV-inducible peroxides and organic free radicals. Exemplarily, the free radicals are generated via photounstable organic UV filters. Similar high levels of peroxides and lipid radicals can be also generated due to other components of a skin care formulation, such as perfumes, or oils. These components are thought to induce Acne aestivalis and photo-and chemo-toxic reactions when exposed to higher levels of UV radiation in sensitive persons [8]. However, in no case the presence of the pure components is responsible for a high Radical Power: Nor the terpene com-ponents of a perfume (e.g. linalool, geraniol, citronellol, limo-nene, among others), nor the pure natural oils (almond oil, sunflower oil, avocado oil, among others) will induce radicals under UV irradiation or adverse skin reactions. In all cases, as to our best knowledge, the hydroperoxide-adducts present in the terpenes or the beginning of rancidity in oils are respon-sible for high RP values.

Conclusion

• Sunscreen formulations using non photo stable filter sys-tems may have a high potential of UV inducible peroxide radicals, expressed by a high RP value.

• Clinical data presented here indicate a clear correlation be-tween the level of UV inducible free radicals and the elicita-tion of Acne aestivalis in sensitive individuals.

• The RP value seems to be a suitable predictive tool for creat-ing sunscreen formulations with low potential of UV induc-ible peroxide radicals and elicitation of Acne aestivalis.

• As a sound formulation strategy it can be recommended to avoid any raw materials with UV inducible peroxide radical potential and/or by adding effective antioxidants to reduce the amount of free radicals.

References

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contact

*Katinka Jung Thomas Herrling

Gematria Test Lab GmbHParkstr. 23 | 13187 Berlin | Germany

**Ulrike Heinrich Hagen Tronnier

DermaTronnier GmbH & Co. KGInstitut für Experimentelle Dermatologie

an der Universität Witten/HerdeckeAlfred-Herrhausen-Str. 44 | 58455 Witten |Germany

***Marcel Schnyder Bernd Herzog

BASF Grenzach GmbH79639 Grenzach-Wyhlen | Germany