A sensitive scalp is one of those conditions that’s easy to dismiss until you’re standing in the shower at 11pm wondering why your head is itching again after washing it with something that cost twenty-three dollars and called itself soothing.

The ingredients in most commercial shampoos, including many marketed as gentle or natural, are more complicated than the label suggests. Fragrance, preservatives, certain surfactants, and high-pH formulas all have the potential to aggravate a sensitive scalp, and they frequently appear together in the same bottle.

This article covers what’s most likely causing the problem, which ingredients to avoid, what to look for instead, and why a well-formulated syndet shampoo bar is often a better starting point than anything on the supermarket shelf. It also covers what a sensitive scalp might signal in some cases, and when to see a professional rather than trying to formulate your way out of it.

If you’re after a deeper looking into what makes the best shampoo for sensitive scalps, read this article.

First: what do we mean by sensitive scalp?

Sensitive scalp isn’t a formal medical diagnosis, it’s a description of a range of symptoms that can have different causes. Itching, burning, redness, flaking, and a feeling of tightness or irritation after washing are the most common presentations. Some people have had symptoms for years and assumed it was just how their scalp works. In many cases, it isn’t.

The most common triggers in shampoo and hair care products are:

Fragrance — consistently identified as the most common allergen in hair care products. A review of patch test results from 226 patients with suspected scalp contact dermatitis, published in the Anais Brasileiros de Dermatologia, found fragrances among the confirmed allergens alongside preservatives and surfactants. Fragrance in a product label can represent dozens of individual chemical compounds, many of which are known sensitisers. Critically, reactions don’t always appear immediately and sensitivity can develop over time with repeated exposure to the same ingredient.

Harsh surfactants — particularly sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES). SLS is an effective cleanser, genuinely good at what it does. The problem is that it does it too well for many scalps. Research has found that SLS and SLES can strip the skin’s hydrolipid layer excessively, disrupting the natural barrier function and leading to dryness, redness, and potential damage. The “squeaky clean” feeling SLS produces is the scalp stripped of oils it needs. For people who don’t have a sensitive scalp, this may be tolerable with regular use. For those who do, it compounds the problem with every wash.

Preservatives — a descriptive analysis of contact dermatitis cases linked to shampoo found preservatives including Kathon CG, formaldehyde-releasing agents, and methyldibromo glutaronitrile among the confirmed allergens. These are standard ingredients in water-based products and aren’t easily avoided in commercial shampoos. Their presence is necessary (water-based products require preservation) but they’re a source of sensitivity reactions.

High pH — traditional soap-based shampoo bars and some commercial shampoos sit at a pH significantly higher than the scalp’s natural range of around 4.5 to 5.5. A high-pH formula opens the hair cuticle, can disrupt the scalp’s acid mantle, and leaves the scalp more vulnerable to irritation. The what pH does to your hair article covers the mechanism in detail.

Scalp conditions including seborrhoeic dermatitis, eczema, and psoriasis can also present with sensitivity symptoms and are worth ruling out if your symptoms are persistent, severe, or spreading. These are medical conditions rather than product sensitivity issues, and a dermatologist is the right starting point — not a new shampoo bar. The advice in this article is relevant to product-related sensitivity, not to managing skin conditions.

Why SLS is worth avoiding for a sensitive scalp

SLS is a powerful anionic surfactant that produces the dense, satisfying lather many people associate with a thorough clean. It’s not a villain in every formula and for people without scalp sensitivity, it works without obvious issue.

For sensitive scalps, it’s a consistent problem. The issue isn’t that SLS is toxic or dangerous at the concentrations used in shampoo, it’s that its cleansing mechanism is indiscriminate. It removes sebum, dirt, and product residue, but it also removes lipids the scalp uses to maintain its barrier function. Ongoing exposure to SLS may compromise the epidermal barrier function, potentially exacerbating skin disorders like dermatitis or eczema by increasing the skin’s sensitivity to irritants.

The scalp compensates by producing more oil, which is why SLS-heavy shampoos can create a cycle of stripping and overproduction that feels like naturally oily hair but is partly a response to the product.

Switching away from SLS doesn’t mean accepting poor lather or ineffective cleansing. It means choosing a surfactant designed to clean without overcleaning.

What SCI does differently

SCI (sodium cocoyl isethionate) is the primary surfactant in the Batch and Bubble syndet shampoo bar formulas. It’s derived from coconut oil and is widely used in products formulated for sensitive skin, including baby care products and dermatologist-recommended cleansers.

The reason for its mildness is rooted in how it interacts with skin at a molecular level. A 2007 study published in the Journal of Cosmetic Science by Ghosh and Blankschtein at MIT demonstrated that SCI is mild and less damaging to the skin barrier than surfactants such as sodium dodecyl sulfate. The researchers found that SCI forms micelles too large to penetrate the aqueous pores of the stratum corneum, meaning it cannot enter the skin layer the way smaller-molecule surfactants can, which is the mechanism behind its well-documented mildness.

In practical terms: SCI cleans effectively without the stripping mechanism that makes SLS problematic for sensitive scalps. The lather is rich and the cleanse is thorough, but the scalp’s lipid barrier is left more intact afterward.

CAPB (cocamidopropyl betaine) is the secondary surfactant in the shampoo bar formulas at Batch and Bubble. It’s worth noting that CAPB appears in sensitivity research as a potential allergen. A study published by the American Contact Dermatitis Society analysing allergen content across best-selling shampoos found CAPB the second most frequently identified allergen.

Importantly, presence in a product is not the same as a high rate of reaction. A separate large-scale patch test analysis of over 83,000 patients found that true allergic reactions to CAPB were rare, with the majority of positive patch test reactions considered likely false positives. CAPB is well-tolerated by the vast majority of users. But if you’ve eliminated fragrance and SLS and still experience reactions, CAPB is worth flagging to a dermatologist for patch testing.

The fragrance question

The Batch and Bubble base formulas contain no added fragrance. So no essential oils, no synthetic fragrance compounds. This was a practical decision from the start: my partner has contact dermatitis triggered by synthetic fragrance, and making products safe for his skin meant eliminating it from the base formula entirely.

It turns out this is also the right call for sensitive scalp formulation. Fragrance is the most consistently identified allergen in hair care, and eliminating it removes the single highest-risk ingredient category in one step. A fragrance-free shampoo bar is the cleanest possible starting point for anyone with scalp sensitivity.

If you want to add fragrance to your own bars, essential oils are an option, but the approach matters. Rinse-off products like shampoo bars have different safety considerations from leave-on products: the contact time is shorter, which affects how sensitising an ingredient can be. That said, some essential oils are known irritants at high concentrations regardless of rinse-off status. The essential oils in shampoo bars article covers which ones I’d recommend, which ones I’d avoid, and the importance of checking maximum usage rates with IFRA guidelines before adding anything to a formula.

If you’re dealing with a sensitive scalp, I’d suggest starting with the fragrance-free base formula and adding nothing until you’ve established that the base is working well. Then introduce one addition at a time with a proper assessment period between each.

The kaolin clay percentage

Kaolin clay in a shampoo bar formula does useful work: it absorbs excess sebum, adds slip, and provides mild cleansing support. For a sensitive scalp, the percentage matters.

At 6.6% (the oily hair formula), kaolin’s absorption is meaningful. For a scalp that isn’t particularly oily and is already dry or irritated, that level of absorption can feel like too much. The dry hair formula uses kaolin at 3%, which provides the slip and texture benefit with less absorption. For a very sensitive, dry, or irritated scalp, 2–3% is a better starting point than 6%.

If you’re adapting any of the Batch and Bubble recipes for a sensitive scalp, reducing the kaolin percentage is the first adjustment worth making alongside keeping the formula fragrance-free.

What an anecdotal observation looks like

My partner has a sensitive scalp and is prone to dandruff. Since switching to the DIY syndet bars (fragrance-free, SCI-based, no SLS, no preservatives) his dandruff has been noticeably less present. I want to be careful here: this is one person, the bars aren’t the only variable, and I’m not in a position to establish cause and effect from a single household observation. But it’s what I’ve seen, and it’s consistent with the reduction in irritant load you’d expect from removing fragrance, SLS, and preservative exposure from a regular routine.

What to look for if you’re buying rather than making

If DIY isn’t your current path, the principles are the same. Look for:

A syndet bar rather than a soap-based bar because the pH will be closer to scalp-friendly from the outset and it won’t react with hard water minerals the way soap does. The are shampoo bars good for your hair article covers this distinction in detail.

Fragrance-free — listed explicitly, not just “naturally scented” or “essential oil-based.” Both can still trigger reactions in sensitive individuals.

SLS and SLES free — check the ingredient list, not the front label claims.

Short ingredient list — fewer ingredients means fewer potential triggers and easier identification of a culprit if something does cause a reaction.

If you are making, find out which formula is your best starting point:

Hard water and sensitive scalp

If you’re in a hard water area and have a sensitive scalp, the two issues can compound each other. Hard water minerals interact with soap-based bar ingredients to leave a film on the hair and scalp that’s difficult to remove and can contribute to irritation. Syndet bars handle hard water better than soap-based bars; why shampoo bars fail in hard water explains the chemistry behind this, but if your sensitivity symptoms seem to worsen after washing rather than improving, water quality is worth investigating alongside product ingredients.

If things aren’t improving

Sensitive scalp symptoms that persist despite switching to fragrance-free, SLS-free products are worth discussing with a dermatologist or GP. Patch testing can identify specific allergens you may be reacting to and is the only reliable way to confirm a contact dermatitis diagnosis. Self-diagnosing scalp conditions and treating them with product changes has limits, the shampoo bar troubleshooting guide can help distinguish product problems from other causes, but it isn’t a substitute for professional assessment if symptoms are ongoing.

Neets is a Brisbane-based home formulator and founder of Batch and Bubble. She has an applied science degree, makes all her own bars, and has a household that has collectively served as a long-running product trial.