Neem oil in soap making
Published by The Soap Brain Team
Neem oil is a conditioning soap-making oil rich in oleic acid (45%). A gram of it turns to soap with about 0.139 g of NaOH (lye). It makes a mild, gentle bar and pairs well with a harder, cleansing oil. Most soapers use it at 3–5% of their oils.
Fatty-acid profile
Neem oil is a gentle, conditioning oil, mostly unsaturated fatty acids that leave a mild, moisturising bar with a softer, lower lather. It pairs naturally with a harder, more cleansing oil to firm the bar up and add bubbles. Because its polyunsaturated (linoleic/linolenic) share is on the higher side, watch the total across the whole recipe and consider a modest antioxidant to guard against rancidity and DOS.
Neem oil is about 38% saturated fat and 60% unsaturated — that unsaturated majority is what makes it conditioning and slower to trace, but softer on its own.
| Fatty acid | Share | What it does in soap |
|---|---|---|
| Oleic acid | 45% | a monounsaturated fatty acid that makes a gentle, conditioning, moisturising bar with a slick, lower lather and a slower trace |
| Stearic acid | 20% | a saturated fatty acid that adds hardness and a thick, stable lather; a large share can speed up trace |
| Palmitic acid | 18% | a saturated fatty acid that builds a hard, long-lasting bar with a stable, creamy lather |
| Linoleic acid | 15% | a polyunsaturated fatty acid that is very conditioning but oxidises readily — a driver of DOS (dreaded orange spots) at high levels |
Neem oil in the bar
Expect a dense, low-bubble, creamy lather from Neem oil — rich and steady rather than foamy. Pairing it with a bubbly oil adds the fluffy bubbles it lacks.
Neem oil traces at a fairly typical pace; how fast the whole batch moves will depend mostly on the other oils, your temperatures and any fragrance you add.
In a blend Neem oil is the conditioning, skin-feel component and can often make up the bulk of the oils. Add a firmer, more cleansing oil — coconut, palm or a hard butter — to bring hardness and bubbles the finished bar would otherwise miss.
Closest substitutes for Neem oil
Out of Neem oil? These oils behave most like it in a bar — ranked by how close their hardness, cleansing and conditioning profile and lye (SAP) requirement are. The numbers are predicted properties for a 100% single-oil bar, not a safety guide; always recalculate the lye when you swap an oil.
| Oil | Hardness | Cleansing | Conditioning | SAP (NaOH) |
|---|---|---|---|---|
| Neem oil (this oil) | 38 | 0 | 60 | 0.139 |
| Lard (pork fat) | 42 | 2 | 54 | 0.139 |
| Emu oil | 30 | 0 | 60 | 0.138 |
| Tamanu (foraha) oil | 30 | 0 | 68 | 0.139 |
| Cottonseed oil | 26 | 1 | 69 | 0.137 |
Using Neem oil in a recipe
One gram of Neem oil needs about 0.139 g of NaOH (sodium hydroxide) to turn fully to soap, within a documented range of 0.135–0.147 g/g across sources. The calculator below uses this value; always confirm the lye weight before you mix.
Its iodine value is about 68 — a moderate value, a good all-round balance of hardness and conditioning. Iodine value is only a rough guide, not a hard rule, but it gives you a feel for how a bar built around this oil will wear.
Most soapers use Neem oil at roughly 3–5% of their oils.
Maker's note: Lard-like base profile, but a strong garlic/black-tea ODOR (sulfur compounds) caps usage at 3–5% for smell, not chemistry. Pair with masking fragrance.
Calculate lye for Neem oil
The calculator below is pre-loaded with Neem oil. Enter your weights, add other oils, and it works out the exact NaOH (lye) weight, water and quality numbers. Always weigh lye, oils and water — never measure by volume, wear gloves and eye protection, and add lye to water (never the reverse).
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Where these numbers come from
Every figure on this page is backed by at least two independent references, listed below — so you can check our work instead of taking our word for it.
- From Nature With Love — Saponification Chart — SAP range
- Classic Bells — Neem oil soap — usage / odor
- RusticWise — Neem oil in soapmaking — composition / usage
- Hamadou et al. (2020), Biomolecules 10(4):616 — Physicochemical characteristics of neem seeds — SAP 199.8–200.1 mg KOH/g (Table 3: 200.090 ± 1.247 and 199.810 ± 1.584 for two seed origins), inside our 189–206 range — so SAP no longer rests on the FNWL chart alone
SAP data last updated · 51 oils covered.
Neem oil soap FAQ
- Can you make soap with 100% Neem oil?
- It is not recommended. Neem oil shows its best in a blend, usually up to about 5% of the oils. On its own the bar would be unbalanced — too soft or low-lathering for everyday use.
- What superfat should I use with Neem oil?
- A 5% superfat is a safe, common starting point for recipes using Neem oil; adjust to taste once you know how the finished bar feels. Never drop to 0% or below without a deliberate reason — the calculator will ask you to confirm it.
- Does Neem oil speed up or slow down trace?
- Neem oil traces at a fairly typical pace; how fast the whole batch moves will depend mostly on the other oils, your temperatures and any fragrance you add.