The Logic of Fragrance in Dish Soap
Liquid dish soap is a surfactant (surface-active, grease-cutting) system designed to break down fats. Fragrance plays a secondary role here; the real work lies in the balance between lather and cleaning performance.
The goal of scenting is not decoration — it is to enhance the sensory experience of use. The sharpness of lemon conveys a "clean" perception; apple softens it. But the fragrance oil must not compromise the clarity or foam of the base formula. Everything beyond that is your signature.
Raw Materials Table
The table below is a balanced starting formula for hand-washing dishes. Foam comes from SLES, mildness from betaine, and viscosity from salt. We have deliberately kept the fragrance oil ratio low.
| Raw Material | CAS No | Ratio | For 100 mL |
|---|---|---|---|
| Deionised water | 7732-18-5 | 65% | 65 mL |
| SLES (sodium laureth sulphate, 70%) | 9004-82-4 | 20% | 20 mL |
| Cocamidopropyl betaine | 61789-40-0 | 8% | 8 mL |
| Sodium chloride (viscosity/salt solution) | 7647-14-5 | 4% | 4 mL |
| Glycerin | 56-81-5 | 2.4% | 2.4 mL |
| Fragrance oil (lemon/apple) | — | 0.5% | 0.5 mL |
| Preservative (e.g. phenoxyethanol-based) | — | 0.1% | 0.1 mL |
| Citric acid (pH adjustment) | 77-92-9 | 0.1% (q.s.) | ~0.1 mL |
The fragrance oil ratio is kept within the 0.2–0.8% range here. Dish soap is formulated for surfaces, not skin; additionally, a high fragrance oil ratio both compromises clarity and needlessly increases cost. d-Limonene (5989-27-5) found in lemon fragrance oils is a natural material with low water solubility; at higher concentrations it increases the risk of cloudiness.
Preparation Steps
Order matters. Add the surfactant to the water, and leave the fragrance oil to last. Mix slowly — fast mixing entrains air, leaving foam in the product that can take days to dissipate.
- Prepare the water base
Measure deionised water into a vessel at room temperature. No heating is required; warm water increases foaming and makes the process more difficult.
- Add the surfactants
Slowly pour in the SLES and stir gently. Once the mixture clears, add the cocamidopropyl betaine. Betaine softens the lather and gives a gentler feel on the skin.
- Adjust the pH
Use a citric acid solution to bring the pH to approximately 5.5–6.5. Correct pH is a prerequisite for proper thickening and skin compatibility.
- Incorporate the fragrance oil
Pre-blend the fragrance oil with glycerin (a pre-mix) and slowly introduce it into the main phase. This helps the fragrance oil disperse more homogeneously. Excess fragrance oil = risk of cloudiness.
- Thicken with salt
Add the sodium chloride solution drop by drop and observe the viscosity. Salt follows a "viscosity curve": beyond a certain point, viscosity actually drops. Do not overshoot that threshold.
- Rest and check clarity
Leave the product in a sealed container at room temperature (~15–20 °C), away from direct light, for 24 hours. Allow air bubbles to escape and clarity to settle. If cloudiness persists, reduce the fragrance oil or re-examine the solubiliser balance.
Safety and the IFRA Framework
Dish soap is not designed for skin, yet skin contact during hand-washing is unavoidable. For this reason, take both product safety and raw material hazards seriously.
Concentrated fragrance oil is flammable. Most aroma chemicals in their pure form have low flash points. Ensure good ventilation while working, avoid static, and always wear gloves and eye protection. Concentrated SLES is irritating if it comes into contact with eyes.
IFRA limits cannot be reduced to a single ratio. Limits vary according to the individual substances/allergens within the fragrance oil (e.g. Limonene, Linalool) and the product category. Dish soap generally falls under the rinse-off product category; even so, always read your fragrance oil's IFRA compliance statement and set your usage level accordingly.
Be equally careful on the labelling and notification side: when bringing a cosmetic or cleaning product to market, the responsible person/manufacturer obligation and the notification process are two separate matters. For current procedures and official fee amounts, refer to TİTCK/ÜTS sources; notification is not free of charge and is subject to official fees.
Troubleshooting, Tips & FAQ
The most common problems tend to cluster around the triangle of fragrance oil ratio, salt balance and pH. The table below is a quick diagnostic guide.
| Symptom | Likely Cause | Solution |
|---|---|---|
| Cloudiness / louching | Fragrance oil ratio too high; water-insoluble materials such as Limonene precipitating as micro-droplets | Reduce fragrance oil to 0.2–0.3%; pre-blend fragrance oil with glycerin; try a suitable solubiliser if needed |
| Phase separation / oily layer on top | Fragrance oil not fully dispersed with the surfactant; solubility limit exceeded | Add fragrance oil in small increments with extended mixing; reduce excess fragrance oil; use a pre-mix |
| Weak scent / short longevity | Fragrance oil level too low, or volatile citrus notes dominating | Bring the ratio towards the upper end of the range; balance with more tenacious apple or green notes |
| Yellowing / colour change | Light and oxidation; natural in citrus fragrance oils in particular | Use an opaque or dark bottle; add a trace amount of antioxidant (BHT, 128-37-0); store in a cool, dark place |
| Consistency too thin or too gel-like | Salt quantity has exceeded the viscosity peak, or pH is incorrect | Adjust pH to 5.5–6.5; add salt drop by drop and stop at the top of the viscosity curve |
| Sediment at the bottom of the bottle | Insoluble waxy or heavy components have settled | Apply cold filtration after chilling (~0–4 °C for 24 hours), then bottle |
Once you have mastered this logic, you have also laid the groundwork for alcohol-based projects. The same solubility discipline will reappear in cologne and body spray formulas, while the ratio-to-concentration balance will come up again in EDP/EDT fragrance work.
How much fragrance oil should I add to dish soap?
Does water prevent cloudiness?
Can I pour the fragrance oil directly into the product?
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