What is propylene glycol?
Propylene glycol (C3H8O2) is a viscous, colorless liquid with a faintly sweet taste. It is a common ingredient used in a variety of industrial and commercial applications. Some of the most common uses of propylene glycol include:
- As a solvent – propylene glycol is able to dissolve many substances, including flavors, food colors, and preservatives.
- As a humectant – propylene glycol helps retain moisture in many cosmetic products, as well as certain foods.
- As an emulsifier – propylene glycol can help evenly disperse ingredients that don’t normally mix together, like oil and water.
- As a carrier – propylene glycol can help deliver active ingredients into the skin, nails, and hair.
- As antifreeze – propylene glycol lowers the freezing point of water, which makes it useful as a component of antifreeze and de-icing solutions.
- As a preservative – propylene glycol inhibits the growth of mold, bacteria, and other microorganisms in pharmaceuticals and cosmetics.
While propylene glycol has many industrial uses, it’s also commonly found in a variety of food products and cosmetics. For example, propylene glycol helps maintain moisture in many baked goods. It’s also used to help evenly distribute flavors and colors in things like salad dressings, yogurt, soda, and artificial sweeteners. In cosmetics, propylene glycol is found in items like shampoo, conditioner, deodorant, and lotion.
Does propylene glycol expire?
Propylene glycol itself does not expire or go bad. As a synthetic substance created through chemical reactions, pure propylene glycol has an indefinite shelf life. However, products containing propylene glycol, such as food, cosmetics, pharmaceuticals, and antifreeze, can degrade over time. Here are some key factors that influence shelf life of products with propylene glycol:
- Exposure to heat and air – Heat and oxygen can accelerate chemical breakdown of products over time, reducing quality and effectiveness.
- Contamination – Introduced microbes or interaction with other ingredients can lead to spoilage.
- Chemical changes – Ingredients may slowly react with each other, altering the product.
- Loss of moisture – Especially relevant in humectant applications, drying out can alter texture and performance.
- Damage to packaging – Compromised containers increase exposure to elements like air and light.
While pure propylene glycol does not have an expiration date, consumers should be aware of expiration dates on any products containing the chemical and discard them after the listed date. Expired items have an increased risk of degradation in quality and effectiveness.
How to tell if propylene glycol is bad
There are a few signs that can indicate propylene glycol-containing products have degraded and may need to be discarded:
- Change in color – Discoloration or darkening can signal chemical breakdown.
- Change in texture – Clumping, thickening, or separation can mean components are separating.
- Change in smell – A rancid or unpleasant odor suggests spoilage.
- Change in taste – An abnormal or bitter taste points to deterioration.
- Change in performance – Products not working as well suggest instability.
- Visible microbial growth – Mold, fungi, and bacteria visible to the naked eye are cause for discarding.
- Damage to packaging – Leaks, rust, expanding containers point to exposure.
Additionally, expiration or best by dates on the packaging should be checked and adhered to. Once a product is past its date, the risk of degradation rises. When in doubt, applying the general rule of thumb, “If in doubt, throw it out” helps avoid consuming spoiled goods.
How to store propylene glycol properly
To help avoid degradation and prolong shelf life, propylene glycol and products containing it should be stored properly:
- Keep in cool area – Store away from direct heat sources like stoves, heaters, or sunlight.
- Avoid temperature extremes – Do not store in freezing temperatures or hot conditions like garages or sheds.
- Keep sealed in original container – Only open container when needing to dispense product to limit air exposure.
- Check for damage – Ensure containers are not leaking and packaging is intact.
- Watch expiration dates – Follow date guidelines and discard expired items.
- Clean storage area – Control dust and pests that could contaminate the product.
- Limit moisture – High humidity can accelerate breakdown in some applications.
- Avoid cross-contaminating – Store chemicals separately from food items.
Propylene glycol as an ingredient has an indefinite shelf life, but once formulated into finished products it can degrade over time. Following manufacturer storage recommendations helps maximize shelf life. Some products may advise refrigeration after opening. Proper storage preserves quality, effectiveness, and safety.
Typical shelf life of propylene glycol products
The shelf life of propylene glycol varies greatly depending on its application and the product formulation. Some typical shelf lives when unopened:
- Food products – Salad dressing, soda, and artificial sweeteners usually last 9-12 months.
- Pharmaceuticals – Oral rinses and non-sterile injections about 2-3 years.
- Cosmetics – Makeup, lotions, and shampoos around 2-3 years.
- Antifreeze/coolant – 2-5 years when ethylene glycol-based.
- E-cigarette liquid – Around 1-2 years recommended.
- Paints and coatings – Oil-based about 5 years, water-based 2-3 years.
However, product shelf lives shorten considerably after opening due to oxygen exposure. Cosmetics and food items usually expire within 6-12 months after opening. Some medications or antifreeze may last 1-2 years after opening.
Following manufacturer guidelines, checking for signs of degradation, and practicing proper storage helps identify if a specific propylene glycol product has expired and needs replacing. When in doubt, prudent discarding of older material helps avoid issues.
Can expired propylene glycol make you sick?
Consuming or using expired products containing propylene glycol does carry some risk of illness or reaction:
- Skin irritation – Outdated cosmetics may result in redness, itching, and swelling if applied.
- Eye irritation – Expired eye drops can cause stinging, watering, and inflammation if used.
- Allergic reactions – Spoiled food and hygiene items may trigger rashes, breathing issues, or anaphylaxis in sensitive individuals.
- Nausea/vomiting – Ingesting rancid or contaminated products may cause temporary gastrointestinal distress.
- Kidney dysfunction – Degraded chemicals in pharmaceuticals can potentially affect kidney health if taken.
- Toxic exposure – Harmful breakdown products or microbial growth could cause poisoning.
However, the risk of severe illness is relatively low in most healthy people. Those with existing kidney impairment or allergies may face heightened risks from degraded chemicals. Very old, compromised antifreeze could potentially be toxic if ingested. But generally, using expired products with propylene glycol would result in mild symptoms that resolve after discontinuing use.
As always, it’s prudent to reference expiration dates and discard products once past their prime. Seeking medical care for persistent symptoms after using an expired propylene glycol item is recommended. Overall though, the risks are moderate and many expired goods may simply be less effective or unpleasant to use.
Can you reuse propylene glycol?
In some applications, propylene glycol can be reused, while other situations require full replacement for safety and performance:
- Vape/e-cig liquids – Should not be reused and replacement is recommended.
- Cosmetics – Reuse not advised due to microbial contamination risks.
- Food products – Should be discarded after opening.
- Antifreeze – Can be reused unless excessively aged or contaminated.
- Pharmaceutical compounds – Consult a pharmacist, but reuse not typically advised.
- Paints/coatings – Reusing and thinning possible if product is stored properly.
Propylene glycol’s solvent properties mean it can pick up impurities easily. Heat, oxygen, and moisture degrade the chemical over time as well. For products where contamination poses health risks like vape liquids, cosmetics, or foods, reuse should be avoided.
However, in systems where the propylene glycol remains sealed and unexposed to extreme conditions, reuse may be possible. This applies primarily to industrial contexts like antifreeze fluid or paints. Again, following storage best practices helps maintain purity for reuse feasibility.
When attempting to reuse propylene glycol, examination for discoloration, stratification, and contamination is prudent. Performance testing a small sample batch is also wise before reintroducing the substance into a large system. And if uncertainty exists at all, replacement is the safest choice.
Disposal guidelines
Propylene glycol-based liquids require some care when disposing to avoid environmental contamination:
- Do not pour down drains, sewers, or into ground soil.
- Mix with inert absorbent material like sand, vermiculite, or kitty litter.
- Place mixed absorbent waste into sealed containers and label.
- Check for local hazardous waste disposal days or sites.
- Contact local municipal waste department for guidance.
- For large commercial volumes, employ a licensed waste disposal service.
- Do not mix with other chemicals.
- Make sure containers are completely emptied before recycling.
Certain jurisdictions may have additional restrictions, such as prohibiting disposal in landfills. Incineration at high temperatures is also an option at approved facilities.
Propylene glycol breaks down easily in nature, but large quantities can impact oxygen levels required by marine life. Following hazardous waste recommendations helps avoid ecological issues while also limiting human exposure.
Conclusion
Propylene glycol is a common, versatile ingredient with a very long shelf life in its pure form. However, once incorporated into finished products, propylene glycol is susceptible to degradation over time from heat, oxygen, light, and microbial growth.
Checking expiration dates, watching for signs like discoloration or smell, and proper storage help preserve shelf life. Outdated propylene glycol may cause mild symptoms if used or ingested, but serious illness is uncommon. Reuse is only appropriate for certain industrial applications where purity can be maintained.
Always reference manufacturer guidelines, exercise caution with outdated product, and discard items at the first sign of deterioration. Employing best practices for storage and disposal protects both human health and the wider environment. With sensible handling, propylene glycol can be safely utilized in a range of everyday goods.
