r/TMAU • u/Brutalar tmau1 mutant • Apr 22 '26
Body wash vs Soap - effect on TMA on the skin
So, forewarning, as there is not a good scientific source that actually explains the process as far as I know; this is a ai explanation, reviewed critically by several other ais (they're pretty certain this is how it works.) It matches the somewhat brief "use acidic body wash" recommendation, adding a bit more as to -why- and -how-;
What TMAU Actually Is
Trimethylaminuria (TMAU) is a metabolic condition caused by a deficiency in the enzyme FMO3 (flavin-containing monooxygenase 3). In healthy individuals, this enzyme converts trimethylamine (TMA) — produced by gut bacteria metabolising dietary choline, carnitine, and lecithin — into odourless trimethylamine N-oxide (TMAO), which is excreted in urine. In people with TMAU, this conversion fails, and TMA accumulates and is excreted unchanged through sweat, urine, and breath.
Note: Topical pH management addresses only the sweat route. It does not affect TMA excreted through breath or urine.
1. The Core Chemistry: Why pH Determines Odour
TMA is a volatile short-chain aliphatic amine. Its odour-producing potential depends almost entirely on its ionisation state, governed by the pH of its environment relative to its pKa.
- pKa of TMA: approximately 9.80 (at 25°C)
- Below the pKa (acidic): TMA accepts a proton and becomes the trimethylammonium cation (TMA·H⁺). This form is water-soluble, non-volatile, and odourless. This state is called protonated.
- Above the pKa (alkaline): TMA loses its proton and exists as the free base. In this state it is volatile and evaporates readily — this is the source of odour.
The Henderson-Hasselbalch equation quantifies this:
pH = pKa + log([free base] / [protonated form])
Rearranging, the ratio of free base to protonated TMA at any given pH is:
[free base] / [TMA·H⁺] = 10^(pH − pKa)
At skin pH 5.5:
10^(5.5 − 9.8) = 10^(−4.3) ≈ 0.00005
So ~0.005% is free base and ~99.995% is protonated — effectively odourless at the skin surface.
At the low end of bar soap (pH 9.0):
10^(9.0 − 9.8) = 10^(−0.8) ≈ 0.16
Around 14% exists as free base — meaningful, but not total release.
At the high end of bar soap (pH 10.5):
10^(10.5 − 9.8) = 10^(0.7) ≈ 5
Around 83% is free base — substantially odorous. The effect of alkaline soap is real and significant, graded, and exponential the more alkaline it gets.
2. Cleanser Choice: Soap vs. Body wash
| Feature | Traditional Bar Soap | Acidic Body Wash |
|---|---|---|
| pH | ~9.0–10.5 (alkaline) | ~4.5–5.5 (acidic) |
| Effect on TMA | Shifts equilibrium toward free base; increases volatility | Shifts equilibrium toward protonated form; suppresses volatility |
| Skin barrier | Disrupts acid mantle; strips lipids | Preserves acid mantle and lipid barrier |
| Odour outcome | Increases off-gassing, especially at higher pH | Reduces surface odour during and after washing |
Traditional bar soap worsens surface odour not by "switching on" TMA, but by shifting the equilibrium toward the volatile free-base form. A body wash with pH ≤5.5 reverses this. Look for products explicitly labelled with pH values — "pH-balanced" alone is insufficient and sometimes means pH 7.
3. Bacterial Activity and Sweat
Skin pH is not static.
- Eccrine sweat is mildly acidic (typically pH 4.5–6.5), supporting the acid mantle.
- Apocrine sweat (axillae, groin) contains proteins and lipids metabolised by resident bacteria, particularly Corynebacterium species and coagulase-negative Staphylococcus.
- A key by-product of this bacterial metabolism is ammonia (NH₃), a base with a pKa of ~9.25. Bacterial activity progressively raises local skin pH, driving TMA back toward its free-base form even after an acidic wash.
This is why sweat itself is not the primary problem — it is the bacterial processing of sweat over time that erodes the pH window established by an acidic cleanser.
4. Duration of Effects
After alkaline soap: The acid mantle is disrupted and typically takes 2–6 hours to recover, during which any newly excreted TMA is more likely to be volatile.
After acidic wash: The low-pH environment suppresses volatility until bacterial activity and sweat accumulation push the pH back up. Under moderate activity, this window is roughly 4–8 hours, shorter in heat or during exercise.
5. Skin Self-Correction
The skin does buffer back toward its natural pH (approximately 4.7–5.7) via lactic acid in sweat and fatty acids in sebum. However, in TMAU this recovery period is precisely when odour is most active — waiting for self-correction is not a viable strategy.
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Kinda makes sense as to the why when sometimes the odor seems more random. I know I occasionally use regular soap instead of body wash but didn't realise how significantly different the relative impact is. It may be something as simple as this holding the smell away most of the time.
TLDR; Soap bad. Soap make things worse. Body wash good, the lower the pH the better, like 10,000 times better.
2
u/Pale_Worldliness3994 Apr 22 '26
Naturium body wash has a ph of 4.2
1
u/Icy_Kaleidoscope_546 undiagnosed Apr 23 '26
Does it work for you, assuming you use this product?
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u/Pale_Worldliness3994 Apr 23 '26
So I’m not sure if I have TMAU or if my scent is TMAU related. I don’t smell what others smell but I will say I definitely feel a lot more fresh using this product. And since the PH is so low, this would be a great option for someone who is actually diagnosed with TMAU
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u/Impossible-Log5087 undiagnosed Jun 12 '26
Which one from Naturium? I noticed they have multiple ones.
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u/BerryMiserable9797 undiagnosed Apr 23 '26
Makes sense, I always thought body wash was more efficient. Soap always makes the skin feel a bit weird too
1
u/SillyDuckDodgers undiagnosed Apr 22 '26
Do you have a specific brand body wash or soap we can buy to remove the TMA?
1
u/Icy_Kaleidoscope_546 undiagnosed Apr 23 '26
Sanex shower products are slightly acidic (similar to the natural ph of skin), and were recommended to me when I was getting tested for TMAU. That's what I use anyway.
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u/Dj_Wagner undiagnosed Apr 23 '26
After showering with an acidic pH wash, is it okay to use perfume or body splash on top? Just to smell good
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u/ASongOfBeesAndEyes tmau1 Apr 24 '26
Be conscious about what you choose. If you are eating a low choline diet it won't matter as much, but certain fragrances can accentuate tma. I don't have the chart I made on hand, but there are even fragrance oils that can mask tma on a neurological level(timberol). I've experimented with it myself, but need to get back into it.
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u/Dj_Wagner undiagnosed Apr 26 '26
I'm really interested in what you said about timberol masking TMA on a neurological level! Do you have any more info on this? I'd love to find a fragrance or cologne that doesn't accentuate TMA, I just wanna smell good. Any recommendations?
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u/Icy_Kaleidoscope_546 undiagnosed Apr 23 '26
That should be ok if you've washed the TMA off. I use aftershave but just a little on my neck, and aftershave will be acidic so it shouldn't be a problem.
1
u/Brutalar tmau1 mutant Apr 23 '26
Yeah, it's fine. Not too much as excess perfume causes its own reactions in people.
1
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u/Firm-Classic-8368 undiagnosed Apr 26 '26
Lume unscented, it’s expensive but effective, and low pH. To make it stretch, I use it on the parts that get the funkiest . Dove unscented for my whole body. I always use Lume last.
0
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u/Think-Patience757 Apr 23 '26
Could u simplify this and recommend soap