Why does one cleaner cut grease and another dissolve scale?

Every cleaner works by matching its chemistry to the dirt in front of you. Acids such as vinegar and citric acid dissolve mineral deposits: hard-water scale, lime around faucets and the chalky part of soap scum. Alkalis such as washing soda and ammonia loosen grease and oily film. Surfactants (soap and detergent) lift oily soil into water so it rinses away. Solvents such as rubbing alcohol dissolve some residues and evaporate. Oxidizers such as bleach and oxygen bleach break down colored stains. Abrasives such as baking soda scrub. This page sorts household dirt into types, shows which kind of ingredient removes each one, and gives the measured pH of common ingredients from their manufacturers' Safety Data Sheets.

The five kinds of household dirt

Most of what you clean falls into a handful of soil types, and each one gives way to a different kind of chemistry.

Loose dust, grit and crumbs are a sixth type that no chemistry is needed for. A dry cloth, vacuum or broom handles them, and removing grit first matters on soft surfaces: the Miracle Sealants Company's stone care booklet names sand, dirt and grit as doing the most damage to natural stone because they are abrasive [11].

What each kind of ingredient does

Acids dissolve minerals

Hard-water scale and lime are carbonate minerals, and acids dissolve carbonates. That is why University of Georgia Extension's green cleaning recipes tell you that hard lime deposits around faucets "can be softened" by covering them with vinegar-soaked paper towels [12]. It is also why acids damage some stone: marble and limestone are calcium carbonate, the same chemistry as the scale, and the stone care booklet warns that acids "will etch or dull the stone surface" [11]. An acid cannot tell the deposit from the countertop.

Acids do little to grease. Spraying vinegar on a greasy range hood mostly moves the grease around.

Alkalis loosen grease

Alkaline ingredients attack fats and oils and help water get under them. New Mexico State University Extension lists washing soda "to cut heavy grease" [13]. The stronger the alkali, the more it does and the harder it is on skin, eyes, aluminum and some finishes. That trade-off runs from baking soda (mild) through borax and washing soda to household ammonia and, at the far end, the lye in commercial oven and drain openers.

Surfactants carry oily dirt into the rinse water

A surfactant is a molecule with one end that holds onto water and one end that holds onto oil. It surrounds oily soil, lifts it off the surface and keeps it suspended so it rinses away. Soap is the oldest surfactant: the federal soap definition describes true soap as a product whose cleaning ("detergent") properties come from "alkali-fatty acid compounds" [14]. Dish liquid uses synthetic surfactants instead. Surfactants are what make protein and general grime come off a counter, and the CDC tells you to clean visibly dirty surfaces with a cleaner containing soap or detergent before you disinfect anything [17]. The surfactants page covers the families for anyone formulating a product.

Solvents dissolve and evaporate

Rubbing alcohol dissolves some sticky and oily residues and evaporates quickly, which is why it appears in streak-free glass recipes. Alliance Chemical's SDS for 91 percent isopropyl alcohol gives a vapor pressure of about 33 mmHg at 20°C [16], high enough that it flashes off a window in seconds. Citrus oils (d-limonene) are solvents too. Solvents bring flammability and, for products you sell, VOC limits, covered on the solvents page.

Oxidizers break down stains

Chlorine bleach and oxygen bleach work by oxidation: they react with the colored compounds in a stain and break them into colorless pieces. That makes them stain removers on fabric and grout, and it is also why they fade dyes and attack some materials. Oxidizers are the most reactive ingredients in a cleaning cupboard, and most of the dangerous combinations on the never-mix list involve one.

Enzymes break down protein and starch

Laundry and dish products often carry enzymes that digest specific soils. Church & Dwight's SDS for an Arm & Hammer plus OxiClean laundry pack lists subtilisins, described as "proteolytic enzymes," that is, enzymes that break down protein [15]. Pantry ingredients have nothing equivalent. Stains are sorted by type on the stain removal page.

Abrasives scrub

Baking soda, salt and scouring powder work mechanically, grinding soil off. NMSU lists baking soda as "a mild abrasive" [13]. Any abrasive can scratch, and on polished stone the booklet tells you not to use scouring powders or creams at all [11].

The pH of common ingredients

pH measures how acidic or alkaline a water solution is: 7 is neutral, lower is acidic, higher is alkaline. Each step is a factor of ten, so a pH of 12 is a hundred times more alkaline than a pH of 10. The figures below are the values the manufacturer printed on each product's Safety Data Sheet (SDS), the hazard document every maker of a workplace chemical must publish. They were measured at different concentrations, so read them as a rough ranking, not a precise comparison.

Two things stand out. Hydrogen peroxide is mildly acidic as sold, which surprises many people. And the gap between baking soda (8.2) and washing soda (11.4) is more than three pH steps, which is why one is a gentle scrub and the other calls for gloves.

pH is not the whole story on hazard. The Vi-Jon SDS classifies its 3 percent peroxide as causing serious eye damage at pH 4.5 [9], and the federal hazard rules for products you sell turn on corrosivity and irritancy rather than a pH cutoff. The pH page covers measuring and setting pH in a product.

Why opposite ingredients undo each other

Because acids and alkalis work on different soils, recipes often combine them, and the two react. Church & Dwight's SDS for baking soda states that it "reacts with acids to yield carbon dioxide" [1], and its washing soda SDS says the same [2]. The fizz is the two ingredients using each other up. What remains is mostly water and a weak salt, with less acid and less alkali than you started with. Soap and acid cancel in a different way: acid turns soap back into the fatty acid it was made from. The combinations page works through each pairing.

Some combinations do something worse than cancel. Bleach with an acid or with ammonia releases toxic gases, and bleach should never be mixed with any other cleaner [17]. Those pairs have their own pages, starting from the never-mix list linked above.

Choosing by the soil in front of you

Name the dirt first, then pick the chemistry:

1. Chalky, white or crusty deposits that come back after drying: mineral scale. Use an acid, on a surface that tolerates acid.
2. Sticky, shiny or smeared film in a kitchen: grease. Use a surfactant first, an alkali for heavy buildup.
3. Food, body soil or general grime: surfactant and water.
4. A colored stain that survives washing: an oxidizer, on a surface and fabric that tolerate it.
5. Grit or crust you can feel: wipe or vacuum first, then a mild abrasive where the surface will not scratch.

The deciding question after that is whether the surface can take it. The surface table sets granite, marble, wood, grout, stainless steel and the rest against acids, alkalis, bleach, alcohol and abrasives.

References

1. Church & Dwight Co., Inc., Material Safety Data Sheet: Sodium Bicarbonate (Baking Soda), MSDS-960, issued January 20, 2009. https://www.physics.purdue.edu/primelab/safety/MSDS/Retired%20SDS%20and%20MSDS/2017%20removed%20safety%20sheets/MSDS%20updated%20to%20SDS/baking%20soda%20%20-%20Arm%20and%20Hammer.pdf
2. Church & Dwight Co., Inc., Safety Data Sheet: Arm & Hammer Super Washing Soda, version 1.0, October 2, 2015. https://uwaterloo.ca/fine-arts/sites/default/files/uploads/documents/arm_and_hammer_washing_soda_10-02-2015.pdf
3. Rio Tinto (Borax Europe Limited), Safety Data Sheet: Borax Decahydrate, Refining Grade, version 1.01, November 18, 2022. https://sds.riotinto.com/display/rtm/FileName-509234
4. Alliance Chemical, Safety Data Sheet: 5% Diluted Acetic Acid Food Grade, revised October 20, 2026. https://docs.alliancechemical.com/sds/5-acetic-acid-food-grade
5. The Clorox Company, Safety Data Sheet: Clorox Regular Bleach2, revision 3, December 9, 2020. https://www.thecloroxcompany.com/wp-content/uploads/2020/12/US001153-Clorox-Regular-Bleach2_3.pdf
6. Church & Dwight Co., Inc., Material Safety Data Sheet: Household Ammonia (Parsons', Bo Peep), MSDS-118, issued October 22, 2007. https://whatsinproducts.com/app/webroot/files/brands_pdf/10189_03005037%20MSDS%20Parsons%20Ammonia.pdf
7. Procter & Gamble, Safety Data Sheet: Dawn Ultra Dishwashing Liquid, Lemon Scent, version 1, October 5, 2015. https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/Dawn%20Ultra%20Dishwashing%20Liquid.pdf
8. Dr. Bronner's, Safety Data Sheet: Tea Tree Pure-Castile Liquid Soap, issued May 24, 2017. https://info.drbronner.com/rsmdocs/msds_biodegradability/liquid-soap-sds-global/teatree_liquid_soap_sds-global.pdf
9. Vi-Jon Inc., Safety Data Sheet: Swan Hydrogen Peroxide 3% (871AA), revision 3, January 8, 2020 (issued January 10, 2020). https://www.rivermuseum.org/sites/default/files/docs/Hydrogen%20Peroxide.PDF
10. Church & Dwight Co., Inc., Safety Data Sheet: OxiClean Versatile Stain Remover, version 4.0, revised August 15, 2022. https://images.thdstatic.com/catalog/pdfImages/fa/fa6c0181-1173-4973-9ead-e5fb14ef73a6.pdf
11. Miracle Sealants Company, Natural Stone Care Made Simple: Caring for Your Stone Installation, 2017 edition. https://www.rustoleum.com/~/media/RustoleumUSA/Pages/miracle-sealants/documents/care_guides/Miracle_Sealants_Company_Basic_Natural_Stone_Care_2017.ashx?la=en
12. University of Georgia Cooperative Extension (Pamela R. Turner and Sharon M. S. Gibson), *Green Cleaning: Recipes for a Healthy Home*, HACE-E-73-1 (Green Clean Booklet), revised October 2018. https://site.extension.uga.edu/greenway/files/2024/09/10.18_Green-Clean-Booklet_update.pdf
13. New Mexico State University Cooperative Extension, Griffiths and Koukel, Green Alternatives to Toxic Household Products and Hazardous Waste (G-313), revised February 2019. https://pubs.nmsu.edu/_g/G313/index.html
14. U.S. Consumer Product Safety Commission, Soap Business Guidance, undated, read October 2026. https://www.cpsc.gov/Business--Manufacturing/Business-Education/Business-Guidance/Soap-Business-Guidance
15. Church & Dwight Co., Inc., Safety Data Sheet: Arm & Hammer Plus OxiClean Ultra Power Power Paks, revised December 2, 2015. https://whatsinproducts.com/app/webroot/files/brands_pdf/1469541633.PDF
16. Alliance Chemical, Safety Data Sheet: Isopropyl Alcohol 91% USP Grade, revised October 21, 2026. https://docs.alliancechemical.com/sds/isopropyl-alcohol-91
17. Centers for Disease Control and Prevention, Cleaning and Disinfecting with Bleach, last reviewed April 24, 2024. https://www.cdc.gov/hygiene/about/cleaning-and-disinfecting-with-bleach.html