What is propylene glycol?
Propylene glycol is a small, synthetic alcohol (chemical formula CH3-CHOH-CH2OH) that has the potential to cause allergic contact dermatitis in some individuals. It is a viscous, colourless, and odourless liquid with low toxicity. Amongst other things, it is used as a humectant, solvent, emulsifier, penetration enhancer and emollient, a food additive, and an intermediate in manufacturing polyester.
Alternative names for propylene glycol include:
- 1,2-propylene glycol.
Propylene glycol was named the American Contact Dermatitis Society’s Allergen of the Year for 2018.
Where is propylene glycol found?
Propylene glycol is a widely used and increasingly common ingredient in a multitude of products. Around 38% of products in the American Contact Dermatitis Society Contact Allergen Management Program (CAMP) database at 2016 contain propylene glycol.
The most common sources of propylene glycol contact allergy are:
- Personal care products (moisturisers, cosmetics, deodorants)
- Topical medications (reported to be the most frequent allergen in topical corticosteroids)
- Some food products
- Electronic cigarettes.
Examples of products that may contain propylene glycol
Personal care products
- Moisturisers, especially gel preparations
- Hair products, including:
- Shampoos and conditioners
- Shaving creams
- Bath salts and oils
- Perfumes and body sprays.
- Topical medicines, including:
- Oral medicines, including:
- Coated pills
- Gel capsules
- Intramuscular and intravenous medications
- Other medical-related products, such as:
- ECG gels
- Ultrasound gels.
- Household cleaners
- Air fresheners
- Laundry detergents
- Printing inks
- Liquid cooling systems/antifreeze
- Food products and beverages
- Electronic nicotine delivery systems eg, e-cigarettes.
Who gets contact allergy to propylene glycol?
Contact allergy to propylene glycol is relatively uncommon. It is estimated to be present in up to 3.5% of individuals investigated for suspected contact dermatitis. Propylene glycol contact allergy may be more prevalent in atopic patients and other patients with compromised skin (such as stasis dermatitis or hand dermatitis). This is noteworthy, given corticosteroids (a common source of propylene glycol contact allergy) are typically first-line treatment for dermatitis.
Allergic contact dermatitis to propylene glycol via occupational exposure is less common, but has been reported in the mechanical and motor vehicle, and printing industries.
What are the features of contact allergy to propylene glycol?
Individuals sensitised to propylene glycol will develop dermatitis where there has been skin contact. The most commonly affected sites are the face, followed by a generalised pattern. Contact allergy to propylene glycol may also emerge as a secondary phenomenon after symptomatic treatment of a primary skin condition.
Propylene glycol is also a common cause of irritant contact dermatitis, and can cause contact urticaria and sensory irritation. Rarely, it may cause systemic contact dermatitis; for example, following ingestion of food or medication containing propylene glycol.
How is contact allergy to propylene glycol diagnosed?
Patch testing is used to diagnose contact allergy to propylene glycol. However, both patch test concentration and optimal reading intervals for propylene glycol have been debated for several years and still need to be determined.
Propylene glycol is included in some standard patch test series. It is important to consider propylene glycol and other allergens not included in all standard series, particularly in patients with atopic or otherwise chronically inflamed skin.
Patch testing details
American Contact Dermatitis Core Series: 30% aqueous solution
NZ Extended Series: 5% petrolatum
Propylene glycol is a weak sensitiser and also an irritant; many reactions are weak (which may be incorrectly interpreted as insignificant) and delineating true allergic versus irritant reactions can be challenging.
Systemic contact dermatitis should be considered if dermatitis fails to clear after avoiding sources of propylene glycol applied to the skin.
How is contact allergy to propylene glycol treated?
As with other contact allergies, once propylene glycol has been identified as a culprit allergen, education and avoidance are the cornerstone of treatment.
Active dermatitis may be treated with:
- Topical steroids
- Calcineurin inhibitors, such as pimecrolimus cream and tacrolimus ointment.
See dermatitis for more information on treatment.
What should I do to avoid propylene glycol?
If you have a contact allergy to propylene glycol, you will need to identify potential sources of propylene glycol and avoid them. This is not an easy task; the key significance of propylene glycol sensitivity rests in how ubiquitous the substance is. Try to use only personal care ingredients with clearly marked ingredients that do not contain propylene glycol (or any of its other names) on the ingredient list. You may need to check with your pharmacist or doctor which topical and other medications will be suitable for you. Your dermatologist may have additional specific advice, particularly if you are highly sensitive to propylene glycol.
If you have an allergy to propylene glycol, you may also be allergic to other common contact allergens, such as balsam of Peru, fragrance mix, benzalkonium chloride (BAK), and/or other topical medicine components eg. bacitracin or neomycin sulfate. These are not cross-reactions. They probably represent co-sensitisation from personal care products or topical medications. Propylene glycol derivatives are potential cross-reactors; further testing is needed.
Polyethylene glycol is not a propylene glycol derivative, and is not a cross reactor.