**5. Dermatological toxicity of essential oils**

In aromatherapy, essential oils, usually diluted in a carrier oil, are applied directly to the skin. The most important dermatological adverse reactions that may occur include irritation, sensitization and photosensitization [18, 19].

**45**

**Figure 2.**

*Safety Profile of Essential Oils*

of adverse reactions [18, 19].

where the essential oil is applied [21].

performed before using these oils.

**5.2 Skin sensitization**

**5.1 Skin irritation**

*DOI: http://dx.doi.org/10.5772/intechopen.91363*

The severity of a dermatological reaction is variable, according to factors like applied substance (aldehydes, phenols), used vehicle, quality/adulteration of the essential oil, method of application, dilution, anatomical site of exposure, integrity of the skin and age of the subject. Environmental conditions could play also an important role. The presence of ultraviolet (UV) light is the decisive factor in photosensitization. Also, ambient temperature and humidity can influence general sensitivity, warm and humid conditions being more favorable for increased severity

Cutaneous irritation is the biological response of the skin to a variety of external

stimuli that can induce skin inflammation. The main pathological mechanisms of irritancy include skin barrier disruption, induction of a cytokine cascade and involvement of the oxidative stress network [20]. Primary irritation (contact dermatitis) occurs rapidly the first time an essential oil is used, manifesting as a red wheal or burn and is more likely to occur when essential oils contain large amounts of compounds like phenol, carvacrol and thymol (oregano, savory or thyme), phenolic ethers like eugenol and anethole (clove) or aromatic aldehydes like cinnamaldehyde (cinnamon) (**Figure 2**). Skin reaction is usually limited to the area

The plants whose essential oils are potentially irritant to the skin are listed in **Table 2**. Considering all these aspects, it is recommended that a patch test should be

In contrast to irritation, skin sensitization is a response of the adaptive immune

system to certain chemical substances called sensitizers or haptens, which can modify skin proteins and induce a delayed T-cell-mediated allergic response [23]. Some of the ingredients which may trigger allergic reactions are listed in the seventh amendment of directive 76/768 CEE (directive 2003/15/CE) and include benzyl alcohol, cinnamyl alcohol, citral, eugenol, hydroxycitronellal, isoeugenol, benzyl salicylate, cinnamaldehyde, coumarin, geraniol, anisyl alcohol, benzyl cinnamate, farnesol, linalool, benzyl benzoate, citronellol, or limonene [24, 25]. Skin sensitization occurs on first exposure to a substance, with only a slight (or absent) effect on the skin. Subsequent exposure to the same compound/compounds will produce a

severe inflammatory reaction caused by T-lymphocytes.

*Chemical structures of the main skin irritant compounds.*

#### *Safety Profile of Essential Oils DOI: http://dx.doi.org/10.5772/intechopen.91363*

The severity of a dermatological reaction is variable, according to factors like applied substance (aldehydes, phenols), used vehicle, quality/adulteration of the essential oil, method of application, dilution, anatomical site of exposure, integrity of the skin and age of the subject. Environmental conditions could play also an important role. The presence of ultraviolet (UV) light is the decisive factor in photosensitization. Also, ambient temperature and humidity can influence general sensitivity, warm and humid conditions being more favorable for increased severity of adverse reactions [18, 19].
