Part of my everyday job involves responding to environmental incidents — fuel spills, soil contamination, groundwater monitoring. You see things in that work that stay with you professionally. You start asking different questions about substances and where they end up.
That habit followed me into formulation — and into how I think about the environmental impact of skincare ingredients.
The Question Nobody in Beauty Asks
Walk into any natural beauty store and you’ll find products promising to be “eco-friendly,” “green,” and “planet-kind.” What you won’t find — on any label, in any marketing campaign — is an answer to this question:
What happens to this product after you rinse it off?
Not what happens to your skin. What happens to the ingredient itself — once it leaves your bathroom, enters the wastewater system, and travels toward the nearest river, lake, or sea.
It’s a question I ask professionally, every day. And it’s one that changes how you read an ingredient list.
Where Your Skincare Actually Goes
When you wash your face or rinse off a mask, everything goes down the drain. But where exactly — and what happens next — depends entirely on the wastewater system that serves your area.
For municipal wastewater — the system most households connect to — treatment typically follows three stages:
- Mechanical treatment — the first stage. Physical processes like screening and sedimentation remove solids, sand, and large particles. Dissolved chemical compounds pass through untouched.
- Chemical treatment — the second stage. Chemical processes remove phosphorus, nitrogen, and other compounds.
- Biological treatment — the third stage. Microorganisms break down organic matter. This is where readily biodegradable ingredients get processed — botanical oils, plant butters, glycerin. Persistent substances like mineral oil, cyclic silicones, or synthetic musks pass through largely unchanged.
Industrial wastewater is a different story. Requirements vary significantly depending on the industry. Some facilities operate only mechanical treatment. Others combine mechanical and chemical. The requirements are tailored to what each industry actually produces — which means cosmetic micropollutants weren’t necessarily part of the design brief.
What this means in practice: the fate of your skincare ingredients in the wastewater system depends on a chain of variables — local infrastructure, treatment level, and the biodegradability of the ingredients themselves.
The only variable you directly control is the last one.
The Croatian Context
According to data published in the journal Hrvatske vode (Pregled stanja pročišćavanja komunalnih otpadnih voda u Republici Hrvatskoj), only 43% of Croatia’s population is connected to any form of wastewater treatment — compared to an EU average of approximately 76%, and over 95% in countries like Denmark, Germany, Austria, and the Netherlands. Croatia ranks at the bottom of the EU alongside Malta and Romania.
On the Adriatic watershed specifically, the predominant treatment level is preliminary treatment with submarine discharge — meaning wastewater receives minimal processing before entering the sea.
In practical terms: if you live on the Adriatic coast, what goes down your drain has a shorter, less filtered journey to the sea than almost anywhere else in the EU.
Biodegradable vs. Persistent — What These Words Actually Mean
In environmental science, we measure biodegradability using standardised tests. The most widely used is the OECD 301 test, which measures how much of a substance breaks down within 28 days under controlled conditions.
A substance that breaks down more than 60% in 28 days is considered readily biodegradable. Microorganisms recognise it as food, and it disappears from the environment relatively quickly.
A substance that doesn’t meet this threshold is considered persistent. It accumulates. It doesn’t disappear. It stays in sediment, in water, in the food chain.
Here’s how that plays out with common skincare ingredients:
| Ingredient | OECD 301 | Classification | Notes |
|---|---|---|---|
| Botanical carrier oils (jojoba, rosehip, sunflower) | ~90% | Readily biodegradable | Fatty acid structure recognised by microorganisms |
| Plant butters (shea, murumuru, cocoa) | Readily biodegradable | Readily biodegradable | Natural triglycerides break down efficiently |
| Petrolatum / mineral oil | ~51% | Not readily biodegradable | Petroleum-derived, persists in environment |
| Cyclic silicones (D4, D5) | <20% | Persistent | Detected in aquatic environments globally |
| Synthetic musks | Persistent | Persistent | Accumulate in aquatic organisms |
| Glycerin | Readily biodegradable | Readily biodegradable | Water-soluble, breaks down quickly |
| Most natural surfactants | Readily biodegradable | Readily biodegradable | Depends on specific compound |
Figures represent orientation values from standardised OECD 301 testing (primarily 301F). Actual degradation rates in the environment vary by conditions, inoculum, and concentration. The category distinction — readily biodegradable vs. not readily biodegradable — is more meaningful than the percentage itself. For substance-specific data, consult ECHA registration dossiers.
Petroleum-Based Cosmetic Ingredients: What the Environmental Data Actually Shows
Cosmetic-grade mineral oil and petrolatum are highly purified. They are safe for skin — hypoallergenic, effective occlusives, sometimes the best clinical option for compromised skin barriers.
But skin safety and environmental fate are two separate assessments.
Mineral oil scores ~51% in OECD 301 testing — below the 60% threshold for “readily biodegradable.” In practice: it passes through wastewater treatment largely unchanged, accumulates in sediment, and forms surface films that affect gas exchange and aquatic life. I work with petroleum derivatives professionally. This behaviour is not surprising — it’s consistent with what we know about hydrocarbon persistence in environmental systems.
That’s not a reason to avoid it at all costs. It’s a reason to know what you’re working with — and to factor environmental fate into formulation decisions, particularly for rinse-off products.
This Doesn’t Mean Natural Is Always Better
I want to be precise here, because environmental science doesn’t deal in simple good/bad categories.
“Natural” doesn’t automatically mean biodegradable — just as “synthetic” doesn’t automatically mean persistent. The extraction process, the supply chain, the concentration in the final formulation — all of these matter.
A 2025 LCA study published in Dermatology and Therapy evaluated cosmetic ingredients across 16 standardised environmental impact categories — including marine ecotoxicity, freshwater eutrophication, and resource depletion. Petrolatum, mineral oils, and cyclic silicones were identified as non-renewable and not readily biodegradable, accumulating in aquatic ecosystems. The study’s substitution table mirrors what’s outlined in this post — botanical oils, sugar-based thickeners, biodegradable polysaccharides. [PMC12454804]
For a deeper look at how natural and synthetic ingredients compare beyond biodegradability, see Natural vs. Synthetic Ingredients in Cosmetics
Ecologist’s Take
When a colleague hands me an SDS for a new substance, I go straight to Section 12 — Ecological Information. Not because it always has answers, but because what it doesn’t say tells me something too.
“No data available” across persistence and degradability, bioaccumulation potential, and ecotoxicity doesn’t mean the substance is safe for the environment. It means the question hasn’t been answered — and that’s worth knowing.
For rinse-off formulations in particular, the environmental fate of every ingredient matters. What passes through the shower drain doesn’t disappear. It enters a system — and depending on where you live, that system may offer very little filtration before it reaches open water.
A Note on UV Filters
UV filters are a clear example of the gap between skin safety and environmental safety. Oxybenzone and octinoxate have been linked to coral bleaching and are persistent in aquatic environments — which is why several countries have banned them outright. For DIY formulators specifically: UV filters require precise dosing, stability testing, and regulatory compliance that goes beyond home formulation.
Read full breakdown in Reef-Safe Sunscreen Guide. For a broader look at which skincare ingredients are safe for the Adriatic specifically, see Sea-Safe Beauty Ingredients: The Adriatic Guide.
Eco-Friendly Alternatives — A Practical Starting Point
If biodegradability matters to you — and after reading this far, I hope it does — here’s a simple reference point for common swaps:
| Ingredient | OECD 301 | Classification | Eco-Friendly Alternative | Alternative Classification |
|---|---|---|---|---|
| Petrolatum / mineral oil | ~51% | Not readily biodegradable | Jojoba wax esters | Readily biodegradable |
| Cyclic silicones (D4, D5) | <20% | Persistent | Plant-derived squalane | Readily biodegradable |
| PEGs (higher MW) | 30–70% | Variable | Decyl glucoside | Readily biodegradable |
| Synthetic musks | Persistent | Persistent | Natural essential oils | Readily biodegradable |
Figures are orientation values. Use as a starting framework, not absolutes.
How to Check Any Ingredient Yourself and whwre to find Environmental impact of Skincare Ingredients
Every cosmetic ingredient supplier is required to provide a Safety Data Sheet (SDS) — a standardised technical document you can request directly from your supplier or download from their website.
For environmental information, go straight to Section 12 — Ecological Information. This section covers:
- 12.1 Toxicity
- 12.2 Persistence and degradability ← most relevant
- 12.3 Bioaccumulation potential
- 12.4 Mobility in soil
- 12.5 PBT and vPvB assessment results
- 12.6 Endocrine disrupting properties
Not all suppliers provide complete data for every point. “No data available” is not the same as “no environmental impact.” It means the question hasn’t been answered — and that’s worth knowing.
So How Can You Actually Know?
Honestly — it’s not always easy. And that’s worth saying directly.
SDS sheets often don’t have the data. Suppliers don’t always know. And “natural” doesn’t automatically mean biodegradable.
A practical hierarchy for finding reliable information:
1. Ask your supplier directly.
Request the SDS and specifically ask if they have OECD 301 biodegradability test results. Not all will have it — but the question itself signals that you care.
2. Check ECHA.
The European Chemicals Agency database contains environmental fate data for many substances. Search by INCI name or CAS number. Section 5 — Environmental Fate & Pathways.
3. Check CosIng.
The EU CosIng database covers cosmetic ingredients specifically.
4. Look for OECD 301 test results.
If a supplier has conducted this test, results may appear in technical datasheets or published literature.
5. Use common sense as a starting point.
Simple plant-derived triglycerides — oils and butters — are generally readily biodegradable. Complex petroleum-derived hydrocarbons — mineral oil, paraffin, petrolatum — generally are not. Silicones — generally persistent. This isn’t a rule, but it’s a reasonable starting framework.
6. Accept uncertainty.
For many ingredients, complete environmental data simply doesn’t exist. The goal isn’t perfection. It’s asking better questions than the label does.
What the EU Is Requiring
The Urban Wastewater Treatment Directive — recently revised — is the EU’s framework for managing what enters and exits our water systems.
Its latest revision introduces, for the first time, a principle of extended producer responsibility for certain industries — including cosmetics and pharmaceuticals. The logic is direct: if your product introduces micropollutants into the water system, you should contribute to the cost of removing them.
This is not yet fully implemented across all Member States. But it is coming.
What it means in practice: the question “where does this ingredient go after it’s rinsed off?” is moving from an ethical consideration to a regulatory one. Brands that can’t answer it will face increasing pressure — from legislation, from consumers, and from the market.
As DIY formulators, this puts you structurally ahead — making ingredient choices today that the industry will be legally required to make within the decade.
The Drain Is Not the End
I work with environmental consequences professionally. I know that what enters a system doesn’t simply disappear — it transforms, accumulates, or passes through. Sometimes it ends up somewhere we didn’t intend.
That knowledge doesn’t make me anxious about my skincare routine. It makes me more intentional about it.
I don’t expect perfection from ingredients — I work in the petroleum industry, I understand complexity and trade-offs better than most. But I do think the question “where does this go?” deserves a place in formulation decisions. Not as a source of guilt, but as a source of information.
As DIY formulators, we’re in a genuinely rare position. We choose every ingredient. We’re not bound by cost-cutting, mass production, or marketing constraints. We can ask the questions that brands don’t — and act on the answers.
That’s not a small thing.
The Adriatic — and every river, lake, and sea that receives what we rinse away — is worth that extra question.
Further Reading
- [Sustainable Beauty Practices]
- [DIY Skincare Ingredients]
- [EU Green Claims Directive: What DIY Makers Need to Know]
- [Botanical Oil Guide]
- [Natural vs Synthetic Ingredients in Cosmetics]
Sources
- Šperac, Obradović, Juretić, Pregled stanja pročišćavanja komunalnih otpadnih voda u Republici Hrvatskojtske vode, 2023
- OECD 301 Biodegradability Test Guidelines
- EU Urban Wastewater Treatment Directive (revised 2024)
- European Chemicals Agency (ECHA)
- Scientific Committee on Consumer Safety (SCCS) — Oxybenzone opinion
- Haykal & Flament et al. — Dermatology and Therapy, 2025. PMC12454804
