• Chemical Name: Citric Acid Anhydrous
• INCI Name: Citric Acid
• Chemical Formula: C₆H₈O₇
• CAS Number: 77-92-9
• E Number: E330
• Molecular Weight: 192.12 g/mol
• Form: Anhydrous (water-free)
• Grade: Food Grade / Pharmaceutical Grade
• Appearance: White to off-white fine crystalline granules or powder
• Odour: Slight citrus / acidic
• Taste: Sharp, sour, strongly acidic
• pH (1% solution in water): Approximately 2.2 — strongly acidic
• pH (0.1% solution in water): Approximately 3.2
• Solubility: Freely soluble in water; soluble in ethanol; sparingly soluble in ether
• Melting Point: Approximately 153°C (decomposes)
• Purity: ≥99.5% Citric Acid Anhydrous
• Water Content: <0.5% (anhydrous form — water-free)
• Heavy Metals: Complies with food grade and pharmaceutical grade specifications
• Storage: Store in a sealed container in a cool, dry place away from moisture, bases, and heat. Keep physically separated from sodium bicarbonate and other carbonates in storage
• Shelf Life: Indefinite when stored correctly in sealed, dry conditions; hygroscopic — will absorb moisture and clump if exposed to humidity

HOW IT WORKS

In Bath Bombs — The Fizz Reaction

Citric Acid + Sodium Bicarbonate + Water → Carbon Dioxide (CO₂) + Water + Sodium Citrate

The CO₂ gas released is what creates the fizz and bubbles. This reaction only occurs in the presence of water — which is why keeping bath bomb mixture dry during making is critical. The standard bath bomb ratio is 1 part citric acid to 2 parts sodium bicarbonate by weight (1:2). At this ratio, all of the citric acid is fully neutralised by the bicarbonate, resulting in a pleasant slightly alkaline bathwater pH.

In Cosmetic Formulation — pH Adjustment

Healthy skin has an acid mantle with a pH of approximately 4.5–5.5. Many cosmetic formulations — particularly water-based lotions, serums, and toners — come out of the mixing process at a higher pH (6–8) that needs to be adjusted downward for optimal skin compatibility and preservative efficacy. A small addition of citric acid dissolved in water and added dropwise to the formulation brings the pH down precisely. Because citric acid is a triprotic acid (three ionisable protons) it is a particularly effective and efficient pH adjuster — a little goes a long way.

In Cosmetic Formulation — Chelation

Citric acid is a chelating agent — it binds to metal ions (particularly calcium, magnesium, and iron) that are present in tap water and some raw ingredients. These metal ions can destabilise emulsions, cause rancidity in oils, and reduce the efficacy of preservatives. Adding citric acid or sodium citrate (the salt formed when citric acid is neutralised) at 0.1–0.5% in water-based formulations improves stability, extends shelf life, and boosts preservative performance.

In Natural Cleaning — Descaling

Limescale and hard water deposits are alkaline mineral compounds (primarily calcium carbonate). Citric acid dissolves them through a simple acid-base reaction — the same chemistry as the bath bomb fizz, but applied to mineral deposits rather than bicarbonate. This is why citric acid is the active ingredient in natural kettle descalers, toilet bowl cleaners, dishwasher cleaning tablets, and showerhead descaling solutions.

RECOMMENDED USAGE RATES

Bath Bombs

• Citric Acid: 25–30% of total dry weight
• Sodium Bicarbonate: 50–60% of total dry weight
• Standard ratio: 1 part citric acid to 2 parts sodium bicarbonate by weight (1:2)
• A 100g bath bomb typically contains approximately 30g citric acid and 60g sodium bicarbonate

Shower Steamers

• Citric Acid: 15–25% of total dry weight
• Sodium Bicarbonate: 60–70% of total dry weight
• Lower citric acid than bath bombs for a slower, more sustained release

Bath Soaks and Effervescent Bath Salts

• Citric Acid: 5–15% of total dry blend for mild effervescence
• Combine with sodium bicarbonate at 1:2 ratio for controlled fizz in bath salts

Cosmetic pH Adjustment

• Typical addition rate: 0.1–2% of total formulation weight
• Dissolve in a small amount of distilled water first to create a 10–50% citric acid solution
• Add dropwise to formulation while monitoring pH with a calibrated meter or strips
• Target pH for skin-safe leave-on products: 4.5–5.5
• Target pH for rinse-off products (shampoo, body wash): 5.0–6.5

Chelation in Cosmetic Formulations

• Usage rate: 0.1–0.5% of total formulation weight
• Add to the water phase before emulsification

Natural Cleaning — Descaling Solution

• General descaling: 1–3 tablespoons per 500ml water; soak or spray and leave 15–30 minutes
• Kettle descaling: 1–2 tablespoons per litre of water; boil and rinse
• Dishwasher cleaning: 2–4 tablespoons in the base of empty dishwasher; run on hot cycle

Laundry and Dishwasher Powder

• Citric Acid: 5–15% of total formulation (acts as water softener and rinse aid)

Food Use (acidulant and preservative)

• Use as per recipe requirements; food grade at this purity
• E number E330 — widely used in food and beverage manufacturing

• The essential acid component of every bath bomb recipe — pairs with sodium bicarbonate to produce CO₂ fizz; cannot be substituted in this application
• Anhydrous form is 100% pure citric acid — more reactive and faster dissolving than citric acid monohydrate, making it the preferred grade for bath bombs and cosmetic pH adjustment
• Food grade and pharmaceutical grade purity — safe for direct skin contact, cosmetic formulation, and food applications
• Highly effective pH adjuster for cosmetic formulations — brings high-pH water-based formulations down to the skin-optimal range of 4.5–5.5 quickly and precisely
• Triprotic acid — three ionisable protons make it a particularly efficient and stable pH buffer at cosmetic use concentrations
• Chelating agent — binds metal ions in hard water to improve emulsion stability, extend shelf life, and boost preservative efficacy in water-based cosmetics
• Effective natural descaler — dissolves limescale, calcium deposits, and hard water stains through acid-base chemistry
• Biodegradable and environmentally safe — naturally derived, septic-safe, and greywater-safe
• Non-toxic at cosmetic and cleaning use concentrations — food grade E330
• Freely soluble in water — dissolves completely and quickly with no residue
• Bulk quantities available — cost-effective for bath bomb businesses, cosmetic formulators, and high-volume users
• Stores indefinitely when sealed and dry — keep away from moisture and bases

TYPICAL APPLICATIONS

• Bath bombs — essential acid fizzing ingredient
• Shower steamers
• Effervescent bath salts
• Cosmetic pH adjustment (serums, toners, lotions, creams, shampoos)
• Chelating agent in water-based cosmetic formulations
• Natural cleaning powders and tablets
• Kettle and coffee machine descaling
• Dishwasher cleaning tablets
• Bathroom and kitchen hard water stain removal
• Toilet bowl cleaning
• Laundry powder (water softening and pH adjustment)
• Food use — acidulant, flavour enhancer, preservative (E330)
• Brewing and wine making (acidity adjustment)
• Pharmaceutical formulations

Food grade — safe for intended cosmetic, cleaning, and food applications at recommended concentrations

Strongly acidic in concentrated form — pH of approximately 2.2 at 1% solution; handle with care in bulk

Avoid contact with eyes — citric acid solutions are irritating to eyes; if contact occurs rinse thoroughly with water for several minutes and seek medical advice if irritation persists

Skin contact at high concentrations or prolonged exposure may cause irritation — always dilute before applying to skin in cosmetic formulations; patch test

May sting or irritate broken, compromised, or very sensitive skin even at cosmetic use concentrations — avoid use on damaged skin

Inhalation of dust in bulk handling — use a dust mask when handling large quantities of powder to avoid respiratory irritation

Food grade but not intended for consumption in large quantities — contact Poisons Information Centre (Australia: 13 11 26) if large amounts are swallowed

Keep away from bases (sodium bicarbonate, sodium carbonate, sodium hydroxide, etc.) in storage — proximity in humid conditions can trigger slow premature reactions; store separately

Hygroscopic — absorbs moisture from air; store in a tightly sealed container in a dry location to prevent clumping and degradation

Keep out of reach of children

Biodegradable and environmentally safe in normal use quantities — suitable for greywater and septic systems

What is the difference between Citric Acid Anhydrous and Citric Acid Monohydrate?
Citric Acid Anhydrous is the pure, water-free form — 100% citric acid by weight. Citric Acid Monohydrate contains one molecule of water per molecule of citric acid, making it approximately 91% citric acid by weight and 9% water. Anhydrous is more reactive, dissolves faster, and is the preferred form for bath bombs, cosmetic pH adjustment, and applications where precise acid concentration matters. If you need to substitute monohydrate for anhydrous in a bath bomb recipe, multiply the anhydrous quantity by 1.10 to compensate for the lower acid content per gram. Our product is Citric Acid Anhydrous.

What is the correct ratio of Citric Acid to Sodium Bicarbonate in bath bombs?
The standard ratio is 1 part citric acid to 2 parts sodium bicarbonate by weight — written as 1:2. In a typical 100g bath bomb this means approximately 30g citric acid and 60g sodium bicarbonate, with the remaining 10g made up of oils, cornstarch, salts, colourants, and fragrance. At this 1:2 ratio all of the citric acid is neutralised by the bicarbonate, producing a pleasantly alkaline bathwater pH comfortable for skin. Some makers use a slightly different ratio — a 1:1.5 ratio produces a more neutral bathwater pH, while more bicarbonate than 2:1 leaves excess unreacted base and a higher final pH.

How do I use Citric Acid to adjust the pH of a lotion or serum?
Dissolve your citric acid in a small amount of distilled water first — a 10–50% solution works well. Make your full formulation, then measure the pH with a calibrated pH meter or pH strips. Add your citric acid solution dropwise while stirring, re-measuring after each addition until you reach your target pH of 4.5–5.5 for leave-on skin care, or 5.0–6.5 for rinse-off products. Add slowly — citric acid is effective and a little goes a long way. Never add dry citric acid powder directly to a finished lotion as it will not distribute evenly.

Why does my bath bomb mixture start fizzing while I am making it?
Premature fizzing is caused by moisture activating the citric acid and sodium bicarbonate reaction before you want it to. Common causes are high humidity in your workspace, wet hands, adding liquid ingredients too quickly or in too large a quantity at once, or using fragrance or carrier oils that contain trace water. Work in a dry space — ideally air-conditioned — use 99% isopropyl alcohol or witch hazel as your liquid binder rather than water, add liquids very slowly in small amounts, and work quickly once any liquids are incorporated.

Can I use Citric Acid Anhydrous in cold process soap making?
Yes, with a specific purpose. Citric acid added to cold process soap at 1–2% of oil weight acts as a chelating agent — it binds calcium and magnesium ions in hard water, improving lather performance and the longevity of the finished bar. However, because citric acid reacts with sodium hydroxide during saponification, you need to add extra lye (sodium hydroxide) to compensate. As a general guide, for every gram of citric acid you add, increase your sodium hydroxide by approximately 0.624 grams above your standard lye calculation. Run your adjusted recipe through a lye calculator to confirm. Citric acid should be added to the oils phase before adding the lye solution.

Is Citric Acid Anhydrous the same as the citric acid I find in supermarkets?
The citric acid sold in small packets in Australian supermarkets for home brewing and cooking is typically Citric Acid Anhydrous at food grade purity — the same grade as our product. The key difference is quantity and value — supermarket citric acid is packaged in small 100g to 500g sachets at a much higher price per kilogram than bulk supply. Our bulk quantities are designed for bath bomb makers, cosmetic formulators, and high-volume users who need consistent food grade purity at a cost-effective price.

How should I store Citric Acid Anhydrous?
Store in an airtight sealed container in a cool, dry location away from moisture. Citric acid is hygroscopic — it absorbs water vapour from the air and will clump and cake if exposed to humidity. Keep it physically separated from sodium bicarbonate and other carbonates in storage — in a humid environment the two can slowly react even without direct mixing. Minor clumping from moisture is normal; break up lumps and sieve before use. Citric acid stored correctly in sealed, dry conditions has an indefinite shelf life.

YOU MAY ALSO NEED

• Sodium Bicarbonate (Food Grade Baking Soda) — the essential partner in every bath bomb recipe; always used alongside citric acid
• Bath Bomb Supplies Collection — shop all bath bomb making ingredients in one place
• Bath Bomb Moulds — 6.5cm round plastic moulds for perfect sphere bath bombs
• Castor Oil (Hexane Free) — skin-conditioning oil addition to bath bomb recipes
• Epsom Salt — blend with citric acid and sodium bicarbonate for muscle-relief bath soaks
• Essential Oils Collection — scent your bath bombs with pure essential oils
• Fragrance Oils — phthalate-free fragrance oils for bath bombs and soaking products
• Colourants — Micas — cosmetic grade mica powders to colour your bath bombs
• Arrowroot Organic Powder — binder and texturiser in bath bomb recipes
• A Guide to Soapmaking Digital PDF — includes bath bomb recipes and formulation guidance