Propylene glycol (PG) is a common synthetic liquid found in many household, cosmetic, and pharmaceutical products, where it serves as a solvent, humectant, and carrier. It is generally considered non-toxic when consumed in small amounts, as the body can efficiently metabolize and excrete it. However, the side effects of propylene glycol can range from mild topical irritation to severe systemic toxicity, depending on the route of exposure, dose, and an individual's underlying health status. Understanding these risks is crucial for both consumers and healthcare providers.
Common Topical Side Effects
For most people, normal topical application of PG-containing products, like cosmetics and moisturizers, does not cause adverse reactions. However, certain individuals, particularly those with sensitive skin or pre-existing conditions like eczema, can experience side effects.
- Skin Irritation: Mild skin irritation, redness, and a burning sensation are common irritant reactions.
- Allergic Contact Dermatitis: More rarely, prolonged or repeated exposure can trigger an allergic reaction, resulting in itchy, inflamed, and blistered skin. PG was even named the American Contact Dermatitis Society's 'Allergen of the Year' in 2018.
- Eye Irritation: Accidental contact with the eyes may cause mild, temporary conjunctivitis.
Risk of Toxicity with High-Dose Exposure
Severe toxicity from propylene glycol is not associated with regular consumer product use but with excessively large or rapidly administered doses, particularly in a medical setting. Patients in intensive care who receive prolonged, high-dose infusions of PG-containing medications (e.g., lorazepam) are most at risk. Toxicity can manifest as serious metabolic, neurological, and cardiovascular issues.
Central Nervous System (CNS) Effects
High systemic levels of propylene glycol can slow down brain activity, leading to CNS depression. In severe cases, this can progress to more serious neurological complications:
- Drowsiness and Confusion: Initial signs of CNS depression.
- Stupor and Coma: A progression of sedation and unresponsiveness.
- Seizures: Can occur as a result of profound neurological disruption.
Metabolic and Organ-Specific Issues
When the body is overwhelmed with high doses of PG, its normal metabolic pathways become saturated. The body converts propylene glycol into lactic acid, and if this buildup is excessive, it causes a severe and potentially life-threatening condition called lactic acidosis.
- Metabolic Acidosis: An abnormal increase in acid in the blood, which can lead to organ dysfunction.
- Hyperosmolality: High concentrations of PG can increase the osmolality of the blood, disrupting the body's fluid balance.
- Acute Kidney Injury: High levels of PG and its metabolites, along with acidosis, can damage the kidneys and impair their function.
Cardiovascular Problems
Cardiotoxicity is another serious risk in cases of high-dose exposure.
- Arrhythmias: Irregular heart rhythms.
- Hypotension: Dangerously low blood pressure.
- Cardiovascular Collapse: Potential for complete circulatory system failure.
Populations at Increased Risk
Several factors can increase a person's vulnerability to PG toxicity, even at lower doses.
- Infants and Young Children: Their bodies have a less-developed alcohol dehydrogenase enzyme system, which is crucial for metabolizing PG.
- Patients with Kidney or Liver Disease: Impaired organ function prevents the body from efficiently processing and excreting PG and its metabolites, leading to accumulation.
- Pregnant Women: Decreased metabolic capacity puts this population at a higher risk.
Propylene Glycol Exposure Risks: A Comparison
| Feature | Low-Dose Consumer Use (Food, Cosmetics) | High-Dose Medical Use (Intravenous) |
|---|---|---|
| Route of Exposure | Oral, Topical | Intravenous (most common in ICU) |
| Primary Risk | Skin irritation, allergic contact dermatitis | Severe systemic toxicity |
| Toxic Accumulation | Very unlikely, rapidly metabolized | Possible with prolonged infusion or impaired organ function |
| Metabolic Impact | Insignificant | Lactic acidosis, hyperosmolality |
| Neurological Effects | None typically reported | CNS depression, seizures, coma |
| Cardiovascular Effects | None typically reported | Arrhythmias, hypotension, cardiac collapse |
| Renal Impact | None typically reported | Acute kidney injury, renal failure |
| Risk Population | Those with skin sensitivities or allergies | Individuals with impaired kidney/liver function, infants |
Conclusion
While propylene glycol is a ubiquitous and useful compound generally considered safe in the low concentrations found in most consumer goods, its potential for side effects should not be overlooked. The risk profile is vastly different between typical exposure and the high-dose, prolonged administration common in clinical settings. Severe PG toxicity, involving metabolic acidosis, CNS depression, and organ damage, is a serious concern, especially for vulnerable populations and patients receiving high-dose intravenous medications. For these at-risk individuals, careful monitoring by healthcare professionals is essential to prevent accumulation and adverse effects. For the general public, awareness of potential skin irritation or allergic reactions is the most relevant consideration.
Learn more about the recognition, treatment, and prevention of propylene glycol toxicity in the medical literature: Recognition, treatment, and prevention of propylene glycol toxicity.
