J. Soc.Cosmet.
Chem.,38, 209-221 (July/August1987)
The effect of solvents on the ultraviolet absorbance
of sunscreens
LOUISE E. AGRAPIDIS-PALOYMPIS
and ROBERT A. NASH,
St.John'sUniversity,
Jamaica,NY 11439, and
NADIM A. SHAATH,* Research
& Development
Laboratory,
FeltonWorldwideInc., Brooklyn,
NY 11237.
Received
March 25, 1987.
Synopsis
Theefficacy
ofsunscreens
isofteninfluenced
bythesolvents
in whichtheyaredissolved.
In thisregard,
the
ultraviolet(UV) absorption
spectra
of 13 UVA andUVB sunscreen
chemicals
weredetermined
in 12
solvents
ofvarying
polarity
andcosmetic
interest.
Changes
in boththewavelength
ofmaximum
absorbance
(K max)andmolarabsorptivity
(½)wereobserved
formanyof thesunscreen-solvent
systems
studied.
Observed
hypsochromic
andbathochromic
shifts
in Kmaxfora number
ofsunscreen
chemicals
wererelated
to theirstructure
andpolarity.Polarsolvents
shiftedtheK maxof polarsunscreens
to shorter
wavelengths
(hypsochromic)
andshifted
lesspolarsunscreens
to longer
wavelengths
(bathochromic).
Ortho-substituted
sunscreen
chemicals,
suchassalicylates
andanthranilates
experienced
a minimumor no UV absorbance
shift.
With theexception
of PABA,mostsunscreens
showed
increased
absorbance
in bothpolarandnon-polar
solvents
and decreased
absorbance
in semi-polar
solvents,suchas hexylene
glycoland C•2-C•5 alcohols
benzoate.
Theresults
of thisstudyshould
aidthecosmetic
chemist
in selecting
appropriate
solvents
andvehicles
for
sunscreen chemicals.
INTRODUCTION
In 1960,Riegelman
andPenna(1) werethefirstto observe
markedchanges
in theUV
absorbance
of p-aminobenzoic
acid(PABA)andseveral
lessimportantUV absorbers
in
five differentsolvents(water,alcoholUSP, polyethylene
glycol400, isopropylpalmirate, andmineraloil). The authorsconcluded
that a sunscreen's
effectiveness
couldbe
influenced
by the solventin whichit is dissolved.
Twelveyearslater,Groves,usinga
thin-filmspectrophotometer,
confirmed
the previous
findingsfor a smallnumberof
sunscreen
chemicals
in polyethylene
glycol400, isopropyl
palmitate,andmineraloil
(2). Shiftsin the spectral
absorbance
of PABAin waterandisopropyl
alcoholwerealso
reportedby Cumpelik(3). Morerecently,Klein andDoshihaveshownthat the UV
absorbance
of severalimportantsunscreen
chemicals,
aloneand in combination
with
* Address
all correspondence
to: Dr. NadimA. Shaath,Technical
Director,FeltonWorldwide,Inc., 599
JohnsonAve., Brooklyn,New York, 11237-USA.
209
210
JOURNAL OF THE SOCIETYOF COSMETICCHEMISTS
eachother, will changeconsiderably
when they are dissolvedin selectedliquid emollients (4).
The presentstudy(5) was undertakento determinethe influenceof 12 cosmeticand
relatedsolventsof varyingpolarityon the UV absorptioncharacteristics
of 13 sunscreen
chemicalsin orderto aid the cosmeticchemistin achievinga betterunderstanding
of
the interactions
that arepossiblebetweenUV absorbers
andliquid components
usedin
sunscreen formulations.
EXPERIMENTAL
MATERIALS
Thirteen sunscreenchemicalswhich are widely used in cosmeticformulationswere
tested.The list includedfive UVA (320 to 360 nm) absorbers
(i.e., menthylanthranilate, oxybenzone,
dioxybenzone,
sulisobenzone,
and butylmethoxydibenzoylmethane)
andeight UVB (290 to 320 nm) absorbers
(i.e., PABA, ethyl dihydroxypropyl
PABA,
octylcyanodiphenylacrylate,
octyl methoxycinnamate,
octyl salicylate,homomenthyl
salicylate,octyl dimethyl PABA, and triethanolamine
salicylate).All of the sunscreens
tested,with the exceptionof butylmethoxydibenzoylmethane,
havebeenassigned
Category 1: safeandeffectivestatusby the FDA over-the-counter
reviewpanel(6).
Twelve solventswerealsoselectedfor study, baseduponeither their usagein cosmetic
formulationor theirpolarity,andarelistedin TableI in decreasing
orderof polarityin
accordance
with Vaughan'ssolubilityparameterassignments
(7).
Chromatographicanalysiswas performedon all sunscreens
and solventsused in the
studyin orderto confirmtheir purity. Our assays
showedthat the materialsusedwere
well within the purity specifiedby the supplier(i.e., not lessthan 98%).
METHODOLOGY
Solutionsfor UV spectralanalysiswere accuratelypreparedusing sunscreen-solvent
Table
I
Solventsand Their Corresponding
SolubilityParameters
Listedin Decreasing
Orderof Polarity
Solubilityparameter
Solvent
Ethanol 70%-water
at 25øC
30%
16.0
10%
13.9
Propylene
glycol
Ethanol 90%-water
14.0
Ethanol
12.8
Hexyleneglycol
Methyl carbitol
12.3
10.7
Ethoxyethanol
Isopropylmyristate
10.6
8.0
Isopropylpalmitate
7.8
C•2-C•5alcohols
benzoate
7.6
Hexane
7.3
Mineral
oil
7.0
SOLVENTS
AND
SUNSCREEN
ABSORBANCE
211
combinations
wherethe solubilityof the sunscreen
waspossiblein the solventat room
temperature.A 50 mg _+ 1 mg sampleof eachsunscreen
wasweighedaccuratelyinto a
100-ml volumetricflaskandthen dilutedto the mark with solvent.The resultingstock
solutionwasthen diluted 1:100 to yield a final sunscreen
concentration
of 5 mg/L.
UV absorbance curves of each final dilution
were obtained with the aid of a Perkin-
ElmerLambda4B UV/VIS spectrophotometer.
A background
correction
wasperformed
using 1-cm quartz cellsfilled with blank solvent.The UV absorbance
curvewasthen
recorded
by scanning
wavelengths
between200 and400 nm, usinga sampleof the final
dilution in the 1-cmquartzcell. The wavelengthof maximumabsorbance
(• max) and
the corresponding
absorbance
valuewere determinedand displayedby the microprocessorunit of the spectrophotometer.
The spectrophotometer's
wavelengthaccuracy
is _+0.3 nm and its absorbance
accuracy
is -+0.005 A when measured at 1,000 absorbanceunit (A). A holmium chloride
standardcell was usedto calibratethe spectrophotometer
and its microprocessor
unit.
Our resultswere within the specifications
establishedfor the standardcell and the
spectrophotometer.
The molar absorptivity(½)wascalculatedfor eachtest solutionat the wavelengthsof
maximumabsorbance
(• max)in the ultravioletregions(UVA, UVB, andUVC). However, only the valuesin the UVA and UVB regionsare reportedin this paper(8).
RESULTS
The ultravioletabsorptionspectralproperties(X max and ½ values)of 13 sunscreen
chemicalsin variouspolar, semi-polar,and non-polarsolventswere obtained. These
data are summarizedin TablesII-IV as three separategroupsof compounds.Sunscreenswhere the • max is shiftedtowardsshorterwavelengths
(hypsochromic
or blue
Table
II
UV SpectralData of Sunscreen
ChemicalsShowingHypsochromic
Shiftsin the •. max
PABA
Solvent
Dioxybenzone
}, max
max
Sulisobenzone
Oxybenzone
½
•. max
½
•. max
ß
9,300
Ethanol 70%-water 30%
266
13,600
326
9,400
324
8,600
321
Propylene
glycol
272
14,500
326
9,100
324
7,500
322
8,400
Ethanol90%-water 10%
Ethanol
271
272
13,800
13,100
326
327
9,400
9,300
325
326
8,900
8,400
324
325
9,500
9,400
Hexyleneglycol
Methyl carbitol
Ethoxyethanol
Isopropylmyristate
Isopropylpalmirate
C•2-C•5alcoholsbenzoate
268
291
293
ins.
ins.
ins.
13,400
18,300
18,900
ins.
ins.
ins.
329
324
325
352
351
352
7,600
8,900
9,600
10,600
10,200
9,900
331
333
334
ins.
ins.
ins.
7,000
5,600
8,500
ins.
ins.
ins.
327
323
327
328
327
328
8,200
8,400
9,000
9,000
9,000
8,300
Hexane
ins.
ins.
351
13,100
ins.
ins.
328
8,800
Mineral oil
ins.
ins.
352
11,400
ins.
ins.
329
7,800
Wavelengthshift from
non-polarto polar solvent
Ah max =
-27nm
Ah max =
-26nm
Ah max =
-10nm
Ah max =
-8nm
212
JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
Table
III
UV SpectralData of Sunscreen
Chemicals
ShowingLittle or No Shiftin the X max
Triethanolamine
salicylate
Octyl
salicylate
Homomenthyl
salicylate
Menthyl
anthranilate
Solvent
X max
E
}x max
E
• max
e
Ethanol 70%-water 30%
298
2,800
308
4,900
306
4,800
336
5,600
Propylene
glycol
298
2,100
307
4,800
307
3,700
335
4,800
297
298
3,000
2,900
305
307
4,000
4,200
305
306
4,300
4,600
337
338
5,000
5,000
Hexyleneglycol
Methylcarbitol
Ethoxyethanol
Isopropylmyristate
Isopropylpalmitate
C12-C•5alcohols
benzoate
298
301
301
ins.
ins.
ins.
2,200
3,100
3,000
ins.
ins.
ins.
306
309
310
309
308
309
3,900
4,000
4,000
4,200
4,600
3,900
306
307
307
308
307
308
2,300
4,800
4,700
5,100
5,000
4,900
339
338
339
338
337
337
4,800
5,700
5,600
4,600
4,700
6,200
Hexane
Mineral oil
ins.
ins.
ins.
ins.
310
310
4,100
4,200
308
308
5,100
4,500
334
334
5,400
6,000
Ethanol 90%-water
Ethanol
10%
• max
e
Wavelengthshiftfrom
A•. max =
A•. max ----
A•. max ----
A•. max =
non-polarto polar
-- 3 nm
-- 2 nm
-- 2 nm
q-2 nm
solvent
shift) in goingfrom non-polarto polarsolventsare listed in Table II. Sunscreens
that
experienced
little or no shift in their }t max in the varioussolventstestedare listed
in Table III. Sunscreens,
where the }t max was shifted towardslonger wavelengths
(bathochromicor red shift), are listed in Table IV. Experimentalvaluescouldnot be
obtainedin thoseinstances
wherethe sunscreen
wasnot solublein the particularsolvent
selectedfor studyand are soindicatedin eachtable.
The change
in thewavelength
of maximumabsorbance
(A }t max)fromtheleastpolar
solvent(i.e., mineral oil) to the mostpolarsolvent(i.e., ethanol70%-water 30%) for
each sunscreenis listed at the bottom of eachtable (II-IV). Where a sunscreenwas
insoluble
in eithera particularpolaror non-polar
solvent,the A }t maxwascalculated
betweenthe leastpolar solventand the mostpolar solventin which the sunscreen
was
soluble.
In addition,selectedUV absorptionspectraof severalof the moreimportantsunscreen
chemicalsin eachcategory(hypsochromic,
bathochromic,
and minimum or no shift),
illustratingthe magnitudeof the shift in the }t max in both polarand non-polarsolvents, are alsopresentedin Figures1-5.
DISCUSSION
CHANGES
IN WAVELENGTH
OF MAXIMUM
ABSORBANCE
In orderfor the cosmeticchemistto estimatethe effectformulationcomponents
haveon
the UV characteristics
of a particularsunscreen
chemical,the polarityof the sunscreen
andthe polarityof the components
in thepreparation
shouldbe determined.
The rela-
SOLVENTS AND SUNSCREEN ABSORBANCE
O-IC'-IC'-IC'-IC'-IC'-IC'-IC'-IC'-IC'-I
_.[_
II
0000
+
II
213
214
JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
r•O
72?
•
t
Absorbance
units
•,
/
'%,.,
//
x,,
/
\
/'
\
,,
/'
100%
ETHYL
ALCOHOL
I"
/
,
!,
588,8
Wavelepgth
(rim}
!
!
!
-6.?62
•
/
/
/
ETHOXY
Absorbance
ETHANOL
units
i
i
Wavelength(rim)
Figure 1. UV absorption
spectra
of PABAshowing
a hypsochromic
shiftin the •. maxin theUVB region
(290 to 320 nm) from a lesspolarsolvent(ethoxyethanol)to a morepolarsolvent(ethanol).
tive lipophilicity,a measureof a compound's
relativepolarity,hasbeendeterminedby
calculatingthe log of the partitioncoefficientbetweenoctanol,a modellipid, andwater
(log P) for 15 sunscreen
chemicals.Thesedata are listed in decreasing
orderof polarity
(i.e., increasinglog P values)in Table V. The log P valueswerecalculatedfrom the
structural
formula
of each sunscreen in accordance with
Rekker's
method
of deter-
SOLVENTS
AND
SUNSCREEN
100%
ETttY•
ABSORBANCE
215
ALCOItOI,
Absorbance
units
-8.881
38g.8
•
488 g
Wavelength
8.7•2
n
units
28e.•
38e•.e
488 e•
Wavelength(nm)
Figure2. UV absorption
spectra
of dioxybenzone
showing
a hypsochromic
shiftin thek maxin theUVA
region(320 to 360 nm) from a non-polarsolvent(hexane)to a polarsolvent(ethanol).
mining hydrophobic
fragmentalconstants
(9). All of the sunscreen
chemicals
included
in this paperare listedin Table V with the exceptionof sulisobenzone.
Nevertheless,
becauseof solubility (Table II) and structuralconsiderations,
sulisobenzone
is consideredto behighlypolar.The datareportedin TableV indicatethat therearetwo groups
of sunscreens:
onethat is morepolar(i.e., log P valuesbetween-0.02 to 2.84) and
the otherthat is considered
to be lesspolar(i.e., log P valuesbetween4.53 and6.08).
The main ingredientin the cosmetic
preparationthat usuallywill causethe k max to
shift is the solventor vehicle.If the solventis very volatile and evaporates
when the
216
JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
100%
ETHYL
ALCOHOL
Absorbance
units
--
W•velength
(nm•)
I
I
!
!
•
i
i
!
•
I
!
I
!
•
I
Absorbancr
units
8.88
Wavelength (nm)
Figure 3. UV absorption
spectraof octylsalicylate
showingno apparentshiftin the X maxin the UVB
region(290 to 320 nm) from a non-polarsolvent(hexane)to a polar solvent(ethanol).
sunscreen
formulationis placeduponthe skin, then other lessvolatileingredientsin
high concentration
will affectthe UV characteristics
of the sunscreen
chemical.
If the sunscreen
is polar(i.e., PABA, dioxybenzone,
sulisobenzone,
and oxybenzone),
then interactionswith polar solventswill causethe UV absorbance
spectrato shift
towardsshorterwavelengths
(TableII andFigure1). Thus PABA becomes
lesseffective
asthe polarityof the solventincreases
and k max shiftsfrom the UVB regionto the
UVC region.In the caseof the threebenzophenones
tested,a hypsochromic
shiftoccurs
within the UVA region.
SOLVENTS
AND
SUNSCREEN
100%
0 425
ETHYL
ABSORBANCE
217
ALCOIIOL
A
Absorbance
units
/
/'
/
Wavelength (nm),
I
-8.415
AL•o•noe
HEXANE
-
units
.0.005
Wavelength (nm)
Figure 4. UV absorptionspectraof octyl p-methoxycinnamateshowinga bathochromic
shift in the
max in the UVB region(290 to 320 nm) from a non-polarsolvent(hexane)to a polarsolvent(ethanol).
On the other hand, if the sunscreen
is lesspolar (i.e., octyl dimethyl PABA, octyl
cyanodiphenylacrylate,
octyl p-methoxycinnamate,
butyl methoxydibenzoylmethane,
and ethyl dihydroxypropyl
PABA), then interactionswith polar solventswill shift the
UV absorbance
spectrato longerwavelengths
(TableIV; Figures4 and5). In the caseof
octyl dimethylPABA, it still remainswithin the UVB regionregardless
of the polarity
of the solvent in which it dissolves.However, as the solvent becomeseither more or less
polar, k max is displacedfrom 308 nm, the wavelengthof optimumprotectionfor a
UVB absorber.In the caseof octyl p-methoxycinnamate,
formulatingwith non-polar
solventsshouldbe avoidedsincesuchsolventswill shiftthe k max awayfrom 308 nm.
218
JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
100%ETHYL
ALCOHOL
,/•'•\,\
Absorbance
units
',--•.--'"-"-",-,.
"•
800
0
.•",./' II
I
•
I
•
I
•
I
•,,
W•vele•th
(nm)l
Absorbance
units
I
I
i
I
•
I
'
,
/,.'I
1
HEINE
,
O
Waveleith (nm)
Figure 5. UV absorption
spectra
of octyldimethylPABAshowinga bathochromic
shiftin the h maxin
the UVB region(290 to 320 nm) froma non-polarsolvent(hexane)
to a polarsolvent(ethanol).
Triethanolaminesalicylate,octyl salicylate,homomenthylsalicylate,and menthyl
anthranilateshowedonly minor variationsin h max in both polarand non-polarsolvents(Table III and Figure 3). The minimum shift of the h max is due to the orthosubstitutedconfiguration
of salicylates
andanthranilates.
The lonepair of electrons
are
involvedin the six-membered
cyclicarrangementand, asa result, are not availablefor
interaction
with polarsolvents
(Figure6). Hence,ortho-substituted
compounds
tendto
exhibit moderateto low • max shiftsin polar solvents.Althoughoxybenzone
and
dioxybenzone
bothmayforma six-membered
cyclicalarrangement,
similarto the salicy-
latesandanthranilates,
theyexhibitaddedpolaritydueto the additionalhydroxyand
methoxygroups.
A more in-depthexplanationfor the shiftsand changesobserved
in the • max that
occurwhen sunscreen
chemicals
aredissolvedin bothpolarand non-polarsolventshas
beenprovidedin separatereportsby Shaath(10, 11).
SOLVENTS
AND
SUNSCREEN
Table
ABSORBANCE
219
V
RelativeLipophilicity of Sunscreen
ChemicalsBasedUpon Their CalculatedPartition Coefficients
Between Octanol
CTFA
Other names
Log P
@25øc
1,2,3-Propanetriol,
1-(4-aminobenzoate)
- 0.02
Sulisobenzone
- 1.51
name
Glyceryl PABA
Benzophenone-4
PABA
Benzophenone-8
Cinoxate
Benzophenone-3
Ethyl dihydroxypropylPABA
Amyl dimethyl PABA
Butylmethoxydibenzoylmethane
Menthyl anthranilate
Octyl salicylate
Homosalate
Octyl methoxycinnamate
Octocrylene
Octyl dimethyl PABA
CHANGES
and Water
IN MOLAR
p-Amino benzoicacid
Dioxybenzone
Ethoxyethylmethoxy cinnamate
Oxybenzone
Ethyl-4-bis(2-hydroxypropyl-aminobenzoate)
Amyl dimethylPABA
Butylmethoxydibenzoylmethane
Menthyl-O-aminobenzoate
2-Ethylhexylsalicylate
Homomenthylsalicylate
Ethylhexyl-p-methoxycinnamate
Octyl cyanodiphenylacrylate
2-Ethylhexyl-p-dimethylaminobenzoate
0.74
2.15
2.55
2.63
2.84
4.53
4.86
5.05
5.30
5.61
5.65
5.69
6.08
ABSORPTIVITY
In additionto shiftsin X max, both increases
and decreases
in the molar absorptivities
(½)of sunscreenchemicalswere alsoobservedin the varioustest solvents.
In general,andwith the exception
of PABA, the restof theUVA andUVB sunscreens
selectedfor studyshowedincreased
½ valuesat X max in both polar(ethanol-water
systems)
andnon-polar
(hexane
andmineraloil) solvents.
In contrast,
thereweresignificant decreasesin ½ values at • max when the sunscreenchemicals were dissolved in
semi-polar
solvents
suchashexylene
glycolandC•2-C•5alcohols
benzoate.
Thesedata
(takenfrom Data TablesII-IV)
havebeensummarizedin TablesVI andVII.
Reduction
in molarabsorptivity
variedbetween12%and55% forhexylene
glycoland
between7% and28% forC•2-C•5 alcohols
benzoate.
In addition,employinga spectrophotometric
technique
suggested
byVogelman
etal. (12),overall
reduction
in thearea
H
6
I
0 -- Menthyl
(a)
ø
I
0 -- Octyl
(b)
Figure6. Stericconfiguration
ofortho-substituted
molecules,
(a)menthyl
anthranilate
and(b)octylsalicylate.
220
JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
Table
VI
Sunscreens
andSolventSystems
That Showed
Changes
in MolarAbsorptivity
Approximate
Sunscreen
Solventexhibiting
Solventexhibiting
increased
decreased
molarabsorptivity
reductionin
molar
molarabsorptivity
absorptivity
UVA Absorbers
Dioxybenzone
Hexane
Sulisobenzone
Menthyl anthranilate
Ethanol 90%-water
Ethanol 70%-water
10%
30%
Butylmethoxydibenzoyl-
Ethanol 90%-water
10%
Ethanol 90%-water
10%
methane
Oxybenzone
Hexyleneglycol
Methyl carbitol
Isopropylpalmitate
Isopropylmyristate
Hexyleneglycol
C12-C15alcoholsbenzoate
40%
37%
25%
25%
24%
24%
Mineral oil
18%
underthe absorbance-vs-wavelength
curveof 32% to 35% wasobserved
for oxyben-
zone,dioxybenzone,
andoctylcyanodiphenylacrylate,
andtherewasa 75% reduction
for triethanolamine
salicylate
in goingfrompolarto non-polarsolvents.
Klein hasrecentlyreported(4, 13) almostcompletesuppression
of UV absorbance
spectra
of octyldimethylPABA,octylp-methoxycinnamate,
andbenzophenones
alone
and in combinationwith eachother in two branched-chain
liquid fatty esters(i.e.,
isostearyl
neopentanoate
and isopropyl
linoleate).Klein'sfindingfor octyldimethyl
PABA in isostearyl
neopentanoate
hasbeenconfirmedin our laboratory.
The principalcharacteristics
of a UV absorption
bandareits position(k max)andits
intensityor molarabsorptivity
(½).In thecaseof thelatter,½values
at k maxofmostof
the sunscreen
chemicalstestedwere greatestin polarand non-polarsolventsand reducedin hexylene
glycolandC•2-C•5alcohols
benzoate.
Drasticreductions
in ½value
Table
VII
Sunscreens
and SolventSystems
That ShowedChangesin Molar Absorptivity
Solventexhibiting
increased
Sunscreen
Solventexhibiting
decreased
molarabsorptivity
molar absorptivity
Approximate
reductionin
molar
absorptivity
UVB Absorbers
PABA
Ethyl dihydroxypropyl
Ethoxyethanol
Ethanol 90%-water 30%
Ethanol
Hexyleneglycol
33%
23%
Ethanol 70%-water
Ethanol 70%-water
Hexyleneglycol
C12-C15alcoholsbenzoate
21%
25%
Methyl carbitol
Hexyleneglycol
Ethanol 70%-water 30%
Hexane
Isopropylmyristate
Hexane
Hexyleneglycol
Hexyleneglycol
29%
20%
PABA
Octyl dimethyl PABA
Octyl p-methoxy
30%
30%
cinnamate
TEA salicylate
Octyl salicylate
Homomenthylsalicylate
Octyl-2-cyanodiphenylacrylate
Ethanol
C12-C15
alcoholsbenzoate
55%
28%
SOLVENTS
AND
SUNSCREEN
ABSORBANCE
221
in suchsemi-polarsolventswould requireincreasingthe concentration
of requiredsunscreenfor maximumprotectionor, in the caseof branched-chain
liquid fatty esters,
replacementwith a moreappropriatesolvent.
In conclusion,
the wavelengthof maximumabsorbance
(h.max)in the UVA and UVB
regionsof the spectrum
andthe resultantmolarabsorptivity
(E)of a sunscreen
chemical
oftenwill be affectedby the solventin which it is dissolved.The changesobservedin
thesetwo importantparameters
appearto be stronglyinfluencedby the polarityand
chemicalstructureof both the sunscreen
and the solvent.The resultsof the present
study of the interactionbetweensunscreens
and solventsprovidepracticalinformation
that cosmeticchemistsmay find usefulin formulatingsunscreen
preparations.
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