Propylene glycol in minoxidil: dermatological side effects and clinical considerations
Propylene glycol is a commonly used excipient in minoxidil solution for hair loss. It acts as a solvent and promotes the absorption of the active ingredient through the skin. However, in some patients, propylene glycol can cause irritant contact dermatitis or allergic contact dermatitis. These reactions are often seen in patients who use minoxidil lotion long-term for the treatment of androgenetic alopecia (AGA). 1–3
In short
For dermatologists, it is relevant that some local side effects of minoxidil are not caused by minoxidil itself, but by the propylene glycol vehicle. In patients with erythema, pruritus, scaling, or a burning sensation of the scalp, it is therefore important to also consider a reaction to the excipient. 1–3
What is propylene glycol?
Propylene glycol is a hygroscopic solvent that is often used as a vehicle in dermatological and pharmaceutical formulations. 1 It occurs in, among others:
- minoxidil solution for hair loss ;
- dermatological creams and ointments;
- shampoos and cosmetic products;
- some oral and intravenous medicines. 4
Propylene glycol has no pharmacological effect on hair growth, but is used to better dissolve active ingredients such as minoxidil and to improve cutaneous penetration.
Irritative dermatitis due to minoxidil lotion
The most common dermatological side effect of propylene glycol is irritant contact dermatitis. 1–3 Clinical symptoms may include:
- pruritus;
- erythema of the scalp;
- burning or stinging sensation;
- scaling or xerosis;
- worsening of existing dermatoses.
These complaints are mainly seen with minoxidil lotions applied twice daily, where the scalp is exposed to propylene glycol for a prolonged period. Patients with seborrheic eczema, a sensitive scalp, or inflammatory skin conditions appear to be more susceptible to these reactions. 1,3
Importantly, the irritation is often caused by the excipient propylene glycol and not by minoxidil itself. 2,3
In patients with a sensitive scalp, it may be beneficial to also consider factors such as seborrheic eczema or scalp scaling. In these situations, treatment of the scalp condition, for example with ketoconazole shampoo in combination with minoxidil , can play a supportive role.
Allergic contact dermatitis caused by propylene glycol
In addition to irritant reactions, propylene glycol can also cause allergic contact dermatitis. 1–3 Clinical features include:
- eczematous skin reactions at the application site;
- erythema, vesicles or edema;
- pronounced pruritus;
- aggravation upon repeated exposure.
The diagnosis can be confirmed by epicutaneous examination (patch testing) by a dermatologist. 1 In case of confirmed allergy, patients should avoid products containing propylene glycol, including cosmetic and pharmaceutical preparations containing this excipient.
Effect on adherence in androgenetic alopecia
Although propylene glycol plays no role in the pathogenesis of androgenetic alopecia, it can indirectly influence treatment effectiveness. 2,3 Three clinically relevant mechanisms are:
1. Reduced adherence to therapy
Local irritation may cause patients to discontinue treatment with minoxidil prematurely.
2. Misinterpretation of symptoms
Inflammation and scaling of the scalp can be accompanied by temporary increased hair loss, which is sometimes interpreted by patients as a worsening of the alopecia.
3. Unjustified intolerance to minoxidil
The intolerance may actually be related to the propylene glycol vehicle and not to the active substance.
Propylene glycol-free minoxidil formulations
Minoxidil formulations without propylene glycol exist, for example foam formulations or alternative vehicles. Studies suggest that some of these formulations have comparable efficacy with better tolerance, particularly in patients with a sensitive scalp. 3
For dermatologists, a propylene glycol-free formulation can be a relevant option for patients who:
- experienced irritation with classic minoxidil lotion;
- prematurely discontinuing therapy;
- have a sensitive scalp.
Systemic safety of propylene glycol
With normal cutaneous use, systemic exposure to propylene glycol is low and generally not clinically relevant in healthy adults. 1 However, caution may be advised in:
- young children;
- patients with severe renal insufficiency;
- patients with severe liver dysfunction;
- patients receiving large amounts of propylene glycol via intravenous medication. 4
With topical application for androgenetic alopecia, systemic toxicity usually plays a limited role.
Practical comparison: lotion versus foam
| Minoxidil lotion | Minoxidil foam | Clinical consideration |
|---|---|---|
| Often containing propylene glycol | Usually propylene glycol-free | Relevant for patients with a sensitive or reactive scalp |
| More frequent irritation in sensitive patients 2,3 | Often better tolerated 3 | Foam can be a better tolerated option for local complaints. |
| Less ideal in case of irritation or scaling | Often more relevant option | Choice of vehicle can influence adherence |
| In case of symptoms, also consider a reaction to an excipient. | Consider in case of irritation or suspected propylene glycol intolerance | Not every side effect can be attributed to minoxidil itself. |
Frequently Asked Questions
Does minoxidil cause scalp irritation?
In some patients, scalp irritation is caused by propylene glycol in minoxidil lotion rather than by minoxidil itself. Propylene glycol can cause irritant contact dermatitis, with symptoms such as erythema, pruritus, and scaling of the scalp. 1–3
What is the difference between minoxidil lotion and minoxidil foam?
Minoxidil lotions often contain propylene glycol as a solvent and penetration enhancer, while formulations within the minoxidil collection may also include propylene glycol-free options. As a result, foam formulations are better tolerated by some patients, particularly those with a sensitive scalp. 2,3
Can propylene glycol cause allergic contact dermatitis?
Yes. Propylene glycol can cause both irritant and allergic contact dermatitis. If an allergy is suspected, a dermatologist can confirm the diagnosis with epicutaneous examination (patch testing). 1–3
What can a dermatologist do for irritation caused by minoxidil?
If scalp irritation occurs during treatment with minoxidil, a dermatologist may consider, among other measures, an alternative formulation without propylene glycol, temporarily adjust or discontinue treatment, and perform patch testing if an allergy is suspected. 1–3
Literature
- Pemberton MA, Kimber I. Propylene glycol, skin sensitization and allergic contact dermatitis: A scientific and regulatory conundrum. Regul Toxicol Pharmacol. 2023;138:105341.
- McGowan MA, Scheman A. Propylene glycol in contact dermatitis: a systematic review. Dermatitis. 2023;34(5):e225–e235.
- Contact Dermatitis Caused by Topical Minoxidil: Allergy or Sensitization to Propylene Glycol? MedRes Arch. 2025;13(4):1–9.
- European Medicines Agency (EMA). Propylene glycol used as an excipient in medicinal products for human use. EMA/CHMP/704195/2013.
