Understanding the Iodine Number in Cosmetics: What It Means for Your Oils

One small number can tell you if your oil will last months or turn rancid in weeks. That’s the power of the iodine number in cosmetics.

If you’ve ever wondered why some carrier oils feel light and silky while others sit on the skin like a rich butter, or why one bottle seems to spoil faster than another, the answer often comes down to this value.

The iodine number (also called iodine value) is a simple measurement of how unsaturated a fat or oil is. In skincare, that translates to three things you care about most: stability, texture, and shelf life.

Understanding this little number means you can choose oils more confidently, create DIY formulations that resist rancidity, and ensure your beauty products last longer without relying on synthetic preservatives. Want to explore the science of plant oils in more detail? Check my Botanical Oil Guide. While the iodine number helps predict oil stability and oxidation, the comedogenic rating shows the likelihood of that oil to clog pores. Used together, they provide a more comprehensive understanding of how an oil behaves in skincare.

👉 In this guide, we’ll unpack what the iodine number means, how it’s calculated, and why it’s a reliable tool for DIY formulators who want to work with oils, fats, and butters in the smartest way possible.

What is the Iodine Number?

Think of the iodine number as your oil’s “unsaturation score.” The higher the score, the more unsaturated fatty acids the oil contains — and the more delicate it tends to be. Unsaturated fatty acids are the building blocks of oils that are more prone to oxidation, making the oil more delicate and susceptible to rancidity.

By definition, the iodine number (or iodine value) measures the amount of iodine in grams that reacts with 100 grams of a fat or oil. In plain words: it tells you how many double bonds are present in the fatty acid chains. More double bonds = more chances for oxygen to sneak in and cause oxidation and rancidity.

Cosmetic formulators and even soapmakers use this value as a guideline to predict how a given oil will behave. Oils with a higher iodine value are generally more prone to oxidation, while those with a lower iodine value are more stable and have a longer shelf life.

It’s important to note that the iodine number isn’t the only stability marker. Other measurements like the peroxide value (which indicates current oxidation level) and the anisidine value (which shows secondary oxidation) can refine the picture. But the iodine number remains the most accessible and widely used factor — especially when comparing different carrier oils and butters.

👉 Keep this in mind: while peroxide and anisidine values show what’s happening now, the iodine number helps you predict what will happen in the future.

Why It Matters in Skincare Formulation

Here’s the fun part: the iodine number isn’t just a boring lab figure — it’s a shortcut to smarter, longer-lasting skincare. In soap making, the iodine number is also used to calculate hardness and conditioning of soaps, but in cosmetics it mainly predicts oxidation and shelf life.

Oils with a high iodine number (like flaxseed or rosehip) are rich in unsaturated fatty acids, which makes them feel light, absorb quickly, and bring amazing skin benefits. The trade-off? They’re susceptible to rancidity and can shorten the shelf life of your DIY products.

On the flip side, oils with a low iodine number (like coconut or jojoba) are packed with more saturated fats. They feel heavier, sometimes even wax-like, but they resist oxidation and keep a formula stable for months.

For DIY formulators, this matters because stability equals trust. Nobody wants to spend time crafting a serum only to find it smells “off” after a few weeks. By checking the iodine value, you can:

• Predict shelf life before even blending your oils.
• Balance textures — lighter feel from high-value oils, richer body from low-value oils.
• Design stable recipes without overloading on fragile ingredients.

In other words, the iodine number helps you determine the right mix of carrier oils, fats, and butters for a product that feels luxurious and holds up against oxidation.

👉 Want to see the difference in action? Next, we’ll look at real examples of oils grouped by iodine number so you can compare stability at a glance.

Iodine Value Examples: Carrier Oils, Fats & Butters

Every plant oil has its own iodine value, influenced by origin, fatty acid composition, and how refined it is. Not all oils are created equal — some are steady workhorses that last for months, while others are delicate divas that demand special care. The iodine number is what separates the two. By looking at this value, you can instantly tell which oils are stable, which ones are moderately fragile, and which need to be used fresh. 

Here’s a quick comparison, organized from the most stable to the most unstable:

👉For a complete overview of more than 70 carrier oils and their profiles, visit my Botanical Oil List.

The rule of thumb:

• Lower iodine value (<100): rich, protective oils and butters → stable, longer shelf life.
• Medium iodine value (100–150): versatile but watch storage and batch size.
• High iodine value (>150): fragile oils with gorgeous skin benefits → best for fresh DIY blends and always stored with extra care.

👉 Keep this table handy as a practical guide when choosing carrier oils. Next, let’s look at how heat sensitivity ties into these numbers and why it matters in your formulations.

Iodine Number and Heat Sensitivity in Formulations

The iodine number doesn’t just predict shelf life — it also tells you how an oil will behave when exposed to heat. The lower the iodine number, the more resilient the oil. That’s why coconut, jojoba, and meadowfoam can handle the heated phase of a formulation without breaking a sweat.

But as the iodine number climbs, those fragile unsaturated bonds make oils more prone to oxidation. Heat accelerates that process, meaning high-value oils lose their beneficial compounds faster. Leave flaxseed oil on heat for too long, and you’ve essentially cut its skincare potential in half.

Here’s a simple breakdown for formulating:

• Low iodine oils (<100): Stable → safe for heating (75–80 °C).
• Medium iodine oils (100–150): Semi-stable → heat gently or add in cool-down.
• High iodine oils (>150): Very delicate → always add in cool-down phase.

Examples in practice:

• Raspberry oil (160–195): Gorgeous for skin but highly unstable → cool-down only.
• Sweet almond oil (~90–100): Low iodine → heat-stable, perfect for emulsions.
• Sunflower oil (118–145): Mid-range → better in cool-down to preserve freshness.

👉 DIY tip: If you absolutely need to warm a sensitive oil, keep the heating time as short as possible and support it with antioxidants such as tocopherol (Vitamin E) or rosemary extract. This simple step can double the oil’s stability and shelf life.

How DIY Formulators Can Use This Number

Here’s where things get practical. Knowing the iodine number gives DIY formulators a secret edge — it’s like peeking into an oil’s future before you even open the bottle.

• Choose stability when it matters most. Working on a cream you want to last for months? Stick with lower iodine oils like coconut, meadowfoam, or jojoba for a longer shelf life.
• Save the delicate divas for special roles. Oils with high iodine values (flaxseed, rosehip, chia) are incredible for skin health but go rancid fast. Use them in small, fresh batches or as part of your cool-down phase.
• Mix and match wisely. Pair fragile oils with stable partners. A drop of flaxseed oil blended with meadowfoam or jojoba can give you the skin benefits without compromising stability.
• Always back them up with antioxidants. Ingredients like tocopherol (Vitamin E) or rosemary extract help extend freshness.
• Store like a pro. Keep oils in dark glass bottles, away from light and heat. Buy in small amounts so you don’t end up with half a bottle going rancid in your cupboard. For a deeper dive, check my guide on How to Store Cosmetics Ingredients.

👉 Think of the iodine number as your DIY insurance policy — it helps you balance texture, shelf life, and beauty benefits so your products feel amazing and stay safe for longer.

Key Takeaways & Practical Tips related to Iodine value

The iodine number is more than a lab figure — it’s your DIY ally. Use it to predict oil stability, balance textures, and extend shelf life.

👉 Want to keep building your formulating skills? Dive into my core resources:

• DIY Skincare Ingredients → learn the building blocks of natural beauty.
• DIY Skincare Recipes → start blending oils with confidence.
• Sustainable Beauty Practices → create products that are kind to your skin and the planet.

FAQ: Iodine Number in Cosmetics

1. What is the iodine value in cosmetics?
The iodine value (or iodine number) is a measurement of how unsaturated a fat or oil is. In cosmetics, it helps formulators determine stability, rancidity risk, and shelf life of carrier oils and butters. A higher iodine value means the oil has more unsaturated fatty acids and is generally less stable.

2. What is a high iodine number?
A high iodine number (above 150) signals that the oil is rich in unsaturated bonds. Oils like flaxseed or chia fall into this range. They feel wonderfully light on the skin but are prone to rancidity and require antioxidants and careful storage to extend freshness.

3. What is a low iodine number?
A low iodine number (below 100) means the oil or fat contains fewer double bonds and is much more stable. Coconut oil, jojoba, and meadowfoam sit in this category. These ingredients resist oxidation and offer a longer shelf life, making them reliable bases for cosmetic formulations.

4. How can you tell if your plant oil is heat sensitive?
Heat sensitivity goes hand in hand with the iodine value. Oils with higher iodine values are more susceptible to oxidation and should be added during the cool-down phase. In contrast, lower iodine oils can handle the heated phase of emulsions at room temperature or above without losing their properties.

5. Why is rosehip oil particularly heat sensitive and why isn’t coconut oil?
Rosehip oil has a high iodine value and is packed with unsaturated fatty acids, which makes it fragile and quick to oxidize. Coconut oil, on the other hand, has a very low iodine value, is mostly saturated, and remains stable even when heated. This contrast is why formulators classify rosehip as delicate and coconut oil as a heat-stable staple.

Conclusion iodine value

At the end of the day, the iodine number in cosmetics is more than a lab value — it’s your guide to choosing oils and fats that bring both beauty and stability to your DIY products. Whether you’re blending light, unsaturated carrier oils or rich, butter-like bases, this simple measurement helps you determine oxidation risk, shelf life, and texture with confidence.

Use it as a reliable guideline, mix delicate oils with more stable ones, and always store your ingredients wisely. That way, every batch you create will feel fresh, effective, and kind to your skin.

Thanks for reading 🌿 Here’s to creating DIY skincare that balances organic beauty, stability, and sustainability — one oil at a time.

With warmth and creativity,
Kristina 🌿