We’ve all been there — the sudden, unpleasant realization that your underarms smell like onions, no matter how fresh your morning routine was. It can be embarrassing, frustrating, and, honestly, just plain annoying. But before you reach for that over-the-counter antiperspirant or douse yourself in a cloud of fragrance, it’s important to understand why this happens in the first place.
The truth is, there’s more to body odour than simply not showering — and sometimes, the cause is more complex than you think. In this article, we’ll dive into 7 surprising reasons why your underarms smell like onions, backed by science, and share how to tackle the issue effectively.
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7 Reasons Your Underarms Smell Like Onions
If your underarms smell like onions — even shortly after showering — you’re not alone. And you’re not dirty. This is a surprisingly common concern rooted in biology, body chemistry, and even lifestyle factors. Here’s what could be happening beneath the surface (or rather, beneath the sleeves).
1. Sulfur-Rich Foods Are Coming Through Your Pores
Certain foods — particularly garlic, onions, broccoli, cabbage, and other sulfur-containing vegetables — can affect more than just your breath. The body metabolizes these foods into compounds such as allyl methyl sulfide, which can’t be fully broken down during digestion.
Instead, these compounds are excreted through your skin and sweat, often accumulating in warm, moist areas like the underarms. If you’ve recently increased your intake of these foods, it could be the reason your underarms smell like onions. This distinctive onion-like scent is a common result of the body’s natural process of releasing these sulfur compounds.
2. Bacteria Are Breaking Down Your Sweat (And Creating Odor Molecules)
Sweat itself is naturally odourless. The problem arises when it meets the diverse bacterial ecosystem living on your skin — particularly in the underarm area.
Certain strains of bacteria, especially Corynebacterium, feed on the lipids and proteins in apocrine sweat. In the process, they produce volatile sulfur compounds — the true source of that unmistakable onion-like odor.
3. Hormonal Changes Can Alter The Composition Of Your Sweat
Hormonal fluctuations — whether due to puberty, menstruation, pregnancy, menopause, or conditions like polycystic ovary syndrome (PCOS) — can change both the amount and the composition of sweat.
Apocrine glands (the ones responsible for underarm sweat) become more active under hormonal influence, increasing the presence of proteins and fatty acids in sweat — which bacteria can rapidly convert into odor-producing molecules.
4. Stress Sweat Contains More Odor-Causing Components
Stress triggers a very specific type of sweat, released from apocrine glands, that is chemically different from heat- or exercise-induced sweat.
This type of sweat is richer in organic compounds like proteins and lipids, providing an abundant food source for odour-causing bacteria. Notably, stress sweat tends to produce stronger and more pungent body odour — often described as sour, sulfurous, or onion-like.
5. Over-Cleansing Or Over-Exfoliating The Underarm Area
While it may seem logical to scrub away underarm odour, excessive cleansing or harsh exfoliation can disrupt the skin’s microbiome, removing beneficial bacteria that help regulate odour and maintain skin barrier function.
This disruption can encourage the overgrowth of more aggressive odour-producing bacteria, exacerbating the problem rather than resolving it.
6. Certain Fabrics Can Trap Odour-Causing Compounds
Synthetic fabrics, particularly polyester and nylon, tend to trap sweat and odor molecules more effectively than natural fibers like cotton or bamboo.
Even after washing, odour-causing compounds can linger in synthetic materials, creating a cycle where clean skin meets not-so-clean clothing — and the onion smell persists.
7. Genetics Play A Role In How (And What) You Smell Like
Individual differences in body chemistry — shaped by genetics, sweat composition, and the delicate balance of your skin microbiome — can make some people more prone to certain types of body odour.
If your underarms smell like onions no matter what deodorant you use, it could be down to your DNA. Some people naturally produce higher levels of sulfur-containing compounds in their sweat, or have a skin environment that encourages the growth of odor-producing bacteria. In these cases, managing odour isn’t just about hygiene — it’s about working with your biology, not against it.
The Best Fix? Meet Nelli Neutralizer Anti-Odor Serum
If you’re ready to stop smelling like an onion factory and start smelling like… absolutely nothing (aka fresh skin), you need to meet Nelli Neutralizer Anti-Odor Serum.
This is not your average deodorant.
The secret to Nelli Neutralizer Anti-Odor Serum isn’t just what it does — it’s how it does it. If your underarms smell like onions no matter what you try, this advanced formula is designed to tackle exactly that. Powered by a synergistic blend of skin-friendly acids, it targets odour at its source while supporting a healthy skin barrier. The result? Fresh, comfortable underarms that stay soft, hydrated, and odour-free — all day long.
Why it’s a game-changer:
- Aluminium-free (no sweat-blocking, no pore-clogging)
- Lets your body sweat naturally (because sweating = healthy)
- Groundbreaking formula designed to LAST ALL DAY — yes, even in hot & humid weather, sports, extreme conditions or for those with hyperhidrosis
- The longest-lasting deodorant you’ll ever find.
The Power of Synergy: A Blend of Acids
1. Glycolic Acid:
One of the most revered ingredients in skincare, glycolic acid works by gently exfoliating the skin and lowering its pH. By doing this, it creates an environment that is hostile to the bacteria responsible for body odour. Glycolic acid’s exfoliating properties also help remove dead skin cells, which further reduces the chances for bacteria to thrive.
2. Lactic Acid:
Lactic acid brings a wealth of benefits, from gentle exfoliation to deep hydration. Unlike harsher acids, lactic acid is incredibly skin-friendly and supports a healthy skin microbiome. It also helps to maintain the skin’s natural moisture balance, ensuring that the skin remains soft, smooth, and irritation-free — even with frequent use.
3. Mandelic Acid:
Derived from almonds, mandelic acid is a gentler exfoliant than many others, making it ideal for those with sensitive skin. It targets odour-causing bacteria without disrupting the skin’s natural barrier. The unique structure of mandelic acid allows it to penetrate the skin more slowly, which also makes it less irritating — a key component in achieving effective yet non-damaging deodorization.
4. Salicylic Acid:
While often associated with acne treatment, salicylic acid also plays a key role in odor control. It works by breaking down the build-up of dead skin cells and oils that can trap bacteria, preventing the formation of odour. Salicylic acid’s anti-inflammatory properties also help soothe the skin, making it especially beneficial for those who suffer from irritation or sensitivity in the underarm area.
5. Gluconolactone:
Gluconolactone is a polyhydroxy acid (PHA) that provides gentle exfoliation while offering powerful antioxidant protection. It hydrates and softens the skin, preventing the dryness or irritation that can sometimes be caused by stronger acids. Additionally, gluconolactone helps to stabilize the skin’s natural pH, ensuring that the formula continues to work effectively without disrupting your skin’s delicate balance.
Skin-Loving Ingredients
Beyond its powerful acid complex, Nelli Neutralizer Anti-Odor Serum is infused with a carefully curated blend of hydrating, soothing, and antimicrobial ingredients — making it far superior to conventional deodorants. This is skincare for your underarms.
Key Supporting Ingredients:
- Aloe Barbadensis Leaf Water — Calms and soothes sensitive skin while delivering lightweight hydration.
- Melaleuca Alternifolia (Tea Tree) Leaf Water — Naturally antibacterial, helping to purify and prevent odour-causing bacteria from thriving.
- Sodium Hyaluronate — A deeply hydrating humectant that draws moisture into the skin, preventing dryness or tightness.
- Dipotassium Glycyrrhizate — Derived from liquorice root, this anti-inflammatory powerhouse helps to calm irritation and support a healthy skin barrier.
Conclusion: Stop the Onion Smell for Good!
If you’ve ever found that your underarms smell like onions, it’s time to understand the science behind it and tackle the issue head-on. By addressing the root causes — from diet to hormones to bacteria — and using a product like Nelli Neutralizer Anti-Odor Serum, you’ll never have to worry about that onion smell again. Embrace fresh, clean, and confident underarms, no matter what life throws your way!
