ABSTRACT
In this chapter, a list of over 110 chemicals identified in essential oils which have reportedly caused contact allergy or allergic contact dermatitis is presented (Table 4.1). Some are well-known allergens; others have caused allergic reactions infrequently, rarely, or even only once. The list includes some compounds that are known allergens in essential oils per se, for example, terpinolene, ascaridole, α-terpinene, 1,2,4-trihydroxymenthane, α-phellandrene, limonene and myrcene in tea tree oil; α-pinene, δ3-carene hydroperoxides and limonene in turpentine oil; geraniol in geranium and rose oils; cinnamic aldehyde in cassia and cinnamon oils; menthol in peppermint oil; carvone in spearmint oil and eugenol in clove oils. The majority of chemicals, however, have caused contact allergy only by their presence in products other than essential oils. When treating patients with allergic reactions to essential oils, the (possible) composition of the oils should be checked first in the individual oil files (Chapters 5.1-5.93). Following that, the list presented here may give some direction to facilitate the search for the responsible allergen(s) in these patients, especially when lack of concomitant reactions to oil ingredients and the nature of the oil composition fail to give proper guidance. Chemicals identified in essential oils which have caused contact allergy/allergic contact dermatitis
Chemical
CAS
CTP
Synonyms and additional information
Refs.
Acetyl cedrene
32388-55-9
Trade name: Vertofix; not found in nature so far
1,2
Ambrettolide
7779-50-2
Synonym: ω-6-hexadecenlactone
3
(E)-Amylcinnamyl alcohol
+
The commercial test preparation is α-amylcinnamic alcohol
4,5
Anethole
104-46-1
+
6,7
Anisyl alcohol
1331-81-3
+
4,5,8
Aromadendrene
489-39-4
9,10
Ascaridole
512-85-6
9,11,12
Azulene
275-51-4
13,14
Benzaldehyde
100-52-7
+
5
Benzoic acid
65-85-0
+
15,16
Benzyl acetate
140-11-4
17
Benzyl alcohol
100-51-6
+
4,5,15,18
Benzyl benzoate
120-51-4
+
4,5,15
Benzyl cinnamate
103-41-3
+
4,5,15
Benzyl propionate
122-63-4
96
Benzyl salicylate
118-58-1
+
4,8,15
Bisabolol
515-69-5
19,20
Bis-(2-ethylhexyl) phthalate
117-81-7
+
Not found in nature so far
104
Butylphenyl methylpropional
80-54-6
+
Trade name: Lilial; not found in nature so far
4
Camphor
76-22-2
+
21,22,23
δ3-Carene
13466-78-9
The allergen is oxidized δ3-carene
24,25,26
Carvacrol
499-75-2
27
Carvone
99-49-0
+
6,9,28,29
β-Caryophyllene
87-44-5
Auto-oxidation increases the sensitizing potency (30,33)
31,32,34
Caryophyllene oxide
1139-30-6
31
1,8-Cineole
470-82-6
35
Cinnamic acid
621-82-9
15
Cinnamic aldehyde
104-55-2
+
Synonyms: cinnamaldehyde, cinnamal; present in the fragrance mix I
4,5,36,37
Cinnamyl alcohol
104-54-1
+
Present in the fragrance mix I
5,15,36
Cinnamyl benzoate
5320-75-2
38
Cinnamyl cinnamate
122-69-0
15
Citral
5392-40-5
+
Combination of neral and geranial; present in the fragrance mix II
39,40,41
42,43
Citronellal
106-23-0
+
44
Citronellol
106-22-9
+
Present in the fragrance mix II; auto-oxidation leads to more sensitizing hydroperoxides (45)
4,36,42
Coniferyl alcohol
458-35-5
15
Coniferyl benzoate
4159-29-9
15
Costunolide
553-21-9
Present in the sesquiterpene lactone mix
46
Coumarin
91-64-5
+
Present in the fragrance mix II
4,36,42
Cuminaldehyde
122-03-2
47
p-Cymene
99-87-6
10
β-Damascone
Contact allergy was to a mixture of α- and β-damascone
32
Dehydrocostus lactone
477-43-0
+
Present in the sesquiterpene lactone mix
48
Dibutyl phthalate
84-74-2
+
Not found in nature so far
101
Diethyl phthalate
84-66-2
+
Not found in nature so far
102,103
Dihydrocoumarin
119-84-6
49
Dimethyl phthalate
131-11-3
+
Not found in nature so far
103
Eugenol
97-53-0
+
Present in the fragrance mix I
4,5,15,36
Falcarinol
21852-80-2
50,51
Farnesol
4602-84-0
+
Present in the fragrance mix II
36,37,42
Geranial
141-27-5
Present in citral (with neral)
40,41
Geraniol
106-24-1
+
Present in the fragrance mix I; auto-oxidation increases the
sensitizing potency (30,52) and leads to the formation of neral and geranial (40)
5,36,37
40,41
Geranyl acetate
105-87-3
44
Guaiazulene
489-84-9
14,53
Heptanal
111-71-7
54
Hexadecanolide
109-29-5
3,55
(Z)-3-Hexenyl salicylate
65405-77-8
56
α-Hexylcinnamaldehyde
101-86-0
+
Not found in nature so far; present in the fragrance mix II
36,37,42
Hydroxycitronellal
107-75-5
+
Not found in nature so far; present in the fragrance mix I
5,36,37
Hydroxycitronellol
107-74-4
Not found in nature so far
57
Hydroxyisohexyl 3-cyclohexene
+
Trade name: Lyral®; not found in nature so far; present in
4,36,97,98,99
carboxaldehyde
the fragrance mix II
α-Ionone
127-41-3
Patients were tested with mixed ionone isomers (47,58)
47,58
β-Ionone
79-77-6
Patients were tested with mixed ionone isomers (47,58)
47,58
Isoeugenol
97-54-1
+
Present in the fragrance mix I
5,36,37
Isoeugenyl acetate
93-29-8
59
Isopulegol
89-79-2
17
Isosafrole
120-58-1
96
Isothymol
4427-56-9
60
Limonene
138-86-3
+
Auto-oxidation increases the sensitizing potency of D-limonene (30) by forming limonene hydroperoxides (63)
37,61,62,64,65
Limonene oxide
1195-92-2
66
Linalool
78-70-6
+
Auto-oxidation increases the sensitizing potency (30) by forming hydroperoxides
4,67,68
Linalyl acetate
115-95-7
Auto-oxidation increases the sensitizing potency (30)
69,70,87
Menthol
89-78-1
+
71,72,73
o-Methoxycinnamaldehyde (2-)
1504-74-1
38
7-Methoxycoumarin
531-59-9
Synonym: herniarin
74
8-Methoxypsoralen
298-81-7
75
Methyl p-anisate
121-98-2
76
Methyl anthranilate
134-20-3
+
77,78
Methyl cinnamate
103-26-4
15,79
Methyl dihydrojasmonate
24851-98-7
Synonym: hedione
32
Methyl eugenol
93-15-2
57
Methylionone
1335-46-2
+
The commercial test preparation is γ-methylionone (α-isomethyl ionone); the patient reacted to ‘methylionone γ’, containing 65-75% α-methylionone (58)
58
Methyl isoeugenol
93-16-3
57
Methyl salicylate
119-36-8
+
80,81
Musk ambrette
123-69-3
+
Not found in nature so far
82,83,84
Myrcene
123-35-3
9,12,31
Neral
106-26-3
Present in citral (with geranial)
40,41
Nerol
106-25-2
57
Nerolidol
7212-44-4
15
Nonanal
124-19-6
54
Nonanol
28473-21-4
54
Nopyl acetate
128-51-8
47
Octanol
29063-28-3
54
α-Phellandrene
99-83-2
9,12,85
2-Phenethyl alcohol
60-12-8
17,47
Phenylacetaldehyde
122-78-1
76,86
α-Pinene
80-56-8
+
Oxidation increases the sensitizing potential
26,85,87
β-Pinene
127-91-3
26,44,82
Piperitone
89-81-6
100
Piperonal
120-57-0
Synonym: heliotropine
17,32
Propylidene phthalide
17369-59-4
76
Pulegone
89-82-7
100
Retinyl (vitamin A) acetate
127-47-9
Not found in nature so far
105
Sabinene
3387-41-5
9
Safrole
94-59-7
7
Salicylaldehyde
90-02-8
+
5,88
Santalol
89-92
α-Terpinene
99-86-5
Auto-oxidation increases the sensitizing potency (30,95)
9,12
Terpinen-4-ol
562-74-3
9,93
α-Terpineol
98-55-5
82,87,94
Terpinolene
586-62-9
9,12,25
Terpinolene
586-62-9
9,12,25
Terpinyl acetate
8007-35-0
17
Thymol
89-83-8
+
23,36,95
1,2,4-Trihydroxymenthane
9,12
Vanillin
121-33-5
+
5
Viridiflorene
21747-46-6
Synonym: ledene
9,12
CTP: Commercial test preparation available (Chapter 3, Table 4)