The Nasties: What They Are, Why They Matter, and How to Avoid Them
You’ve probably seen the word “nasties” scattered across skincare and aromatherapy websites. It’s become a kind of shorthand — a promise that a brand doesn’t use certain ingredients. But what exactly counts as a nasty, and how can anyone be sure their products are genuinely free from them?
The truth is that nasties aren’t one single thing. They’re a mix of contaminants, adulterants, unsafe essential oils, synthetic fillers, and degraded ingredients that can quietly slip into products without being declared. Some are harmful to the environment, some can irritate skin, and some can cause real toxicity if used incorrectly. And yes — some still appear in animal products, where regulations are weaker.
The impact varies from person to person. A baby, for example, is far more vulnerable than a healthy adult. But the principle remains the same: you deserve to know what’s in the bottle.
Why Nasties Matter
Nasties matter because they can:
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Undermine therapeutic value
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Increase allergy or toxicity risks
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Mislead customers
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Damage trust in the aromatherapy industry
In aromatherapy, the issue falls into two main areas:
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Pure Essential Oils
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Carrier bases — creams, lotions, gels, and oils
Some essential oils sold online should never be used. Others require careful handling, especially for sensitive individuals and animals. And some cosmetic ingredients deserve to be avoided altogether.
The Nasties Found in Aromatherapy Products
The nasties we’re talking about are the hidden, often undeclared substances that can end up in essential oils and wellness products. These include phthalates, synthetic fragrance additives, oxidised allergens, toxic essential oils, and even heavy metals.
At Us Them and U, we’ve traded for 37 years without a single health-related complaint. That’s because we only sell fresh, batch-controlled, high quality essential oils and carriers, and we make sure our safety advice is clear, honest, and accessible.
Essential Oils We Recommend You Do Not Use at All
Some essential oils carry significant toxicity risks and are not suitable for general aromatherapy:
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Parsley Herb Oil (Petroselenium crispum)
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Pennyroyal Oil (Mentha pulegium)
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Savin Oil (Juniperus sabina)
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Tansy Oil (Tanacetum vulgare)
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Wintergreen Oil (Gaultheria procumbens)
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Wormwood Oil (Artemisia absinthium)
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Rue (Ruta graveolens)
These oils appear in old herbal texts and online marketplaces, but they have no place in modern safe practice.
Phototoxic Essential Oils
Some essential oils contain furanocoumarins (FCs) — compounds like bergapten and psoralen that react with UV light and can cause burns or pigmentation.
Phototoxic oils include:
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Bergamot (cold pressed) — the most phototoxic. Our Bergamot is FC Free
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Lime (cold pressed)
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Lemon (cold pressed)
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Grapefruit (cold pressed)
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Bitter Orange
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Cumin
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Rue — extremely phototoxic; avoid in skincare
Steam-distilled citrus oils are generally safe because the FCs don’t carry over.
Ingredients We Recommend You Avoid
Sulphates
SLS and SLES can irritate skin and are produced via polluting processes. None of our products contains SLS or SLES.
Parabens
Effective preservatives, but their safety continues to be reviewed. We do not use parabens.
Other Nasties You May Find in Aromatherapy Products
Phthalates
Endocrine disruptors that can enter oils through plastic equipment or adulteration.
Synthetic fragrance additives
Often hidden behind “parfum”. These can trigger headaches, allergies, and respiratory irritation.
Heavy metals
Nickel, cadmium, arsenic, mercury — usually from polluted soils or poor processing. Some samples exceed EU medicinal plant limits.
Oxidised terpenes
Even pure oils become “nasty” when oxidised. Limonene, linalool and others form sensitising by-products that irritate skin and lungs.
VOCs & secondary pollutants
All essential oils emit VOCs. When terpenes react with indoor ozone, they can form formaldehyde. Long diffusion sessions (>1 hour/day) increase respiratory load.
But here’s the key: fresh, well stored oils behave very differently from degraded ones.
How to Reduce VOC Problems
Prevent oxidation
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Store oils in dark glass, tightly sealed
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Keep away from heat and sunlight
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Replace citrus oils every 12–18 months
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Avoid diffusing near open windows on high ozone summer afternoons
Diffuse safely
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Diffuse for 15–30 minutes, then switch off
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Leave 1–2 hours between sessions
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Avoid continuous diffusion
Improve ventilation
Ventilation is the single most effective way to reduce VOC concentration.
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Crack a window
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Use an extractor fan
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Keep doors open
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Avoid tiny enclosed rooms
Adulteration with cheap carrier oils
Low grade vegetable oils, mineral oil, or synthetic esters reduce therapeutic value and increase irritation.
Mislabelled or incorrect species
A widespread issue:
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“Lavender” sold as lavandin
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“Sandalwood” sold as amyris
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“Rosewood” replaced with synthetic linalool
Avoid “fragrance oils” marketed as aromatherapy
If it says “parfum”, “fragrance”, or “aroma blend”, assume synthetics.
A Final Note
The world of aromatherapy is rich, beautiful, and deeply rooted in nature — but it’s also full of complexity. It’s easy to get lost in chemistry, regulations, and research papers. If the subject interests you, there is plenty more to explore, and yes, even books worth reading.
For now, the simplest truth is this: Freshness, honesty, and proper sourcing matter more than anything else.
