Citric Acid: The Spark Behind the Fizz

There is something wonderfully satisfying about dropping a bath bomb into water and watching it come alive.

The fizz. The bubbles. The gentle release of fragrance and colour.

Behind that familiar reaction is a simple piece of formulation chemistry: citric acid.

A naturally occurring organic acid found in citrus fruits and many other plants, citric acid has become an important ingredient in cosmetics and personal care. In bath products, its most recognisable role is as one half of the acid-and-alkali combination responsible for the characteristic fizz of a bath bomb.

It may not be the most glamorous ingredient in the formulation.

But it certainly earns its place.

INCI Name

Citric Acid

Citric acid is a naturally occurring organic acid found in fruits and other plant materials.

Despite its association with lemons and other citrus fruits, cosmetic-grade citric acid is commonly produced commercially through fermentation, rather than being extracted directly from large quantities of citrus fruit.

Citric acid is also an alpha hydroxy acid (AHA). However, its role in a bath bomb or bath salt is very different from the role of a deliberately formulated facial or body exfoliant containing an AHA.

Origin

Citric acid occurs naturally in a wide range of plants, particularly citrus fruits such as lemons and oranges.

The compound was first isolated from lemon juice in the eighteenth century. Today, commercial citric acid is predominantly manufactured through microbial fermentation of carbohydrate sources, followed by purification and crystallisation.

This production method allows consistent, high-purity citric acid to be produced for applications across food, pharmaceuticals, cosmetics and household products.

In bath formulations, its most familiar role is not about its origin in citrus at all.

It is about what happens when it meets the right partner.

Key Skin Benefits

Citric acid has several cosmetic functions, but in Bareglow bath products its most important role is formulation functionality.

• Creates the characteristic bath bomb fizz
When citric acid reacts with sodium bicarbonate in the presence of water, the two ingredients undergo an acid-base reaction that releases carbon dioxide gas.

Those escaping bubbles are what create the familiar fizz of a bath bomb.

• Helps create an enjoyable bathing experience
The fizzing reaction helps disperse fragrance, colour and other ingredients throughout the bathwater, contributing to the sensory experience of the finished product.

• Can function as a pH adjuster
Citric acid can be used in cosmetic formulations to help adjust and control pH. The appropriate amount depends on the complete formulation rather than on citric acid alone.

• Has exfoliating properties in specific formulations
Citric acid is an AHA and, at suitable concentrations and pH levels, can contribute to chemical exfoliation. However, this should not be confused with the role citric acid plays in a bath bomb.

The distinction is important.

An ingredient can have several cosmetic functions without performing all of them in every product.

In a Bareglow bath bomb, citric acid is primarily there to help create the fizz.

How It's Used

Citric acid is widely used in bath bombs, bath tablets, bath powders, cleansers, creams and other cosmetic formulations.

For bath bombs, it is commonly combined with sodium bicarbonate.

When the dry ingredients are kept away from water, they remain relatively stable. Once the finished bath bomb is placed in water, the acid and sodium bicarbonate dissolve and react, producing carbon dioxide.

The basic reaction can be represented as:

Citric acid + sodium bicarbonate + water → carbon dioxide + water + sodium citrate

The proportions matter.

Too little citric acid can affect the fizzing performance, while too much can alter the product's behaviour and potentially affect skin comfort. Moisture control during manufacturing and storage is also important because premature exposure to water can begin the reaction before the product reaches the bath.

This is a good example of why thoughtful formulation matters.

The ingredient itself is simple.

Getting the balance right is the craft.

Cautions

Citric acid is widely used in cosmetic products, but its effects depend heavily on concentration, pH and the type of finished product.

• Do not apply concentrated citric acid directly to the skin.

• Higher concentrations can be irritating, particularly when the pH is sufficiently low.

• Do not assume that citric acid in a bath bomb acts as a skin exfoliant. The finished product, dilution in bathwater and resulting pH are very different from a deliberately formulated AHA treatment.

• Avoid contact with the eyes. If product enters the eyes, rinse thoroughly with clean water.

• Take care with broken or significantly irritated skin, where acidic products may cause stinging or discomfort.

• Control moisture during manufacturing and storage. Water can trigger the reaction between citric acid and sodium bicarbonate prematurely, affecting the performance and stability of bath bombs.

• Use cosmetic-grade citric acid from a suitable supplier and formulate according to the requirements of the finished product.