Soap is always a good choice, period!

Soap is naturally readily biodegradable and always a good choice, regardless of who made it. If the choice is between soap and something else, choose soap. The other option may not be bad either, but make it a habit not to choose chemicals you do not know everything about. If there is anything in the ingredients list that you feel unsure about, look it up or choose something you know what it is. A warning symbol is there for a reason.

If you have made it this far on your journey toward chemical awareness, you have come further than most! 
Congratulations, great job! You have done yourself, your health, your family’s health, your immediate environment, and the climate a great service.

If you want to go even further, some of us are so "nerdy" that we like to calculate and examine things, so of course there are differences between soaps too.

Soaps have different properties depending on which oil or fat is saponified. Some fats, such as linseed oil and rapeseed oil, produce fatty soaps that treat and nourish wood, while tall oil, for example, produces a slight excess of fat that does not have the same nourishing properties.
Tall oil is a by-product of the pulp industry (paper mills). More precisely, tall oil is extracted as a by-product of the kraft process in paper production.

 The process requires several chemicals:

 

• Sodium hydroxide (lye) and sodium sulfide are used to cook wood chips and separate lignin from cellulose.

• Sulfur dioxide and other sulfur compounds are used in the paper mill’s process and contribute to sulfur emissions.

• Tall oil soap, which is formed during the process, must be treated and further refined to become usable tall oil.

 

 

Presence of rosin, a resin acid found in tall oil that may also occur in tall oil soap. People can be contact-allergic to the resin acids in rosin and may then develop itchy rashes and eczema. For example, its presence in printing on clothes can cause a rash. Using many sticky notes, for example, can trigger eczema because the rosin is present in the adhesive. The adhesive in ordinary plasters often contains resin acids; if you are hypersensitive, you should instead choose a plaster with a different adhesive, such as one with acrylic adhesive. According to issue no. 1, 2025, of the Asthma and Allergy Association's magazine, YDMA, the Occupational and Environmental Dermatology Department at Skåne University Hospital in Malmö, found that 75% of defence recruits at several regiments in Skåne developed contact allergies from the foot tape used by the armed forces to prevent chafing during marches. The contact allergy was caused by rosin in the foot tape. This is serious because rosin also contains substances that can make people allergic to perfume, fragrances, and wood materials.

From a climate and environmental perspective, there are a few additional aspects to consider; below is a comparison table addressing various factors.

 

Factor Circulated rapeseed oil (e.g. recycled frying oil) Tall oil (a by-product of the paper industry) CO₂ emissions (kg CO₂-eq/kg) ~0.1–0.3 (for collection and purification) ~0.2–0.6 (depending on the process and transport) Energy consumption (MJ/kg) Low (only for collection and purification) Higher due to heating and refining Agricultural land No new land required No new land is needed; however, forestry and its consequences should be considered from both a climate and environmental perspective. Water consumption Minimal High in paper mill processes Chemical use None additional Sodium hydroxide (NaOH), sodium sulfide (Na₂S), sulfur dioxide (SO₂), tall oil soap Biological impact Reduces waste, no impact on ecosystems Affects forest ecosystems through logging Processing steps Filtration and cleaning Chemical separation, heating, and refining Availability and circularity Limited to the amount of recycled oil Limited to the forestry industry's production

 

 

Soy is sometimes used to make soft soap, often deck soap. Soy-based soap has certain disadvantages, primarily problems related to biodiversity and rainforest destruction. Feel free to ask at your building supply store which oil your deck soap is based on. 
Other problematic circumstances include:

 

• Pesticides and artificial fertilisers are used in large quantities when growing soybeans, particularly in South America, where soy cultivation is expanding into cleared rainforest.

 

• Hexane, a fossil-based solvent, is often used during oil pressing to maximise extraction. It is a volatile organic compound with health risks and environmental impacts.

 

• Artificial fertilisers and pesticides contribute to nitrogen leakage, soil acidification, and affect ecosystems.

 

Factor Circulated rapeseed oil (e.g. recycled frying oil) Soybean oil (newly produced from soybeans) CO₂ emissions (kg CO₂-eq/kg) ~0.1–0.3 (collection and purification only) 4–6 kg (due to logging, cultivation, processing) Energy consumption (MJ/kg) Low (collection and filtration) High (cultivation, harvesting, refining, transportation) Agricultural land No new land required Approx. 0.7–1.2 m² per kg of oil, often in sensitive areas Water consumption (liters/kg) Minimal Approx. 2,300–3,500 liters per kg (large water footprint) Chemical use None additional Pesticides, chemical fertilizers, hexane (solvent used in extraction) Biological impact Reduces waste, no impact on ecosystems Deforestation, loss of biodiversity, erosion Processing steps Simple filtration and purification Cultivation, harvesting, solvent extraction, refining Availability and circularity Limited to the amount of recycled oil Large-scale but linked to negative environmental effects

 

 

Below is a comparison table that also includes flaxseed oil. Flaxseed oil has a relatively low CO2 impact and also requires little cultivation area; however, much of the flax used for flaxseed oil production is grown in Russia and China, which could possibly be considered a problem, if not for any other reason, then from a shipping perspective. 

 

Property	Recycled rapeseed oil	Tall oil	Soybean oil	Flaxseed oil
Biodegradable	Yes	Yes	Yes	Yes
Origin	Plant-based (rapeseed)	Wood-based (by-product)	Plant-based (soybeans)	Plant-based (flaxseed)
Environmental impact	Low, recycled material	Moderate, by-product of the forestry industry	High, linked to deforestation	Low, requires licultivation area
CO₂ emissions (kg CO₂-eq/kg)	~0.1–0.3	~0.2–0.6	4–6	~0.2–0.5
Energy consumption (MJ/kg)	Low	High	High	Moderate
Agricultural land	No new land required	No new land required	Approx. 0.7–1.2 m²/kg	Small cultivation area
Water consumption	Minimal	High	2,300–3,500 liters/kg	Low
Chemical use	None additional	NaOH, Na₂S, SO₂	Pesticides, hexane	None additional
Biological impact	Reduces waste	Affects forest ecosystems	Deforestation, erosion	No deforestation, low impact
Processing steps	Filtration and cleaning	Chemical separation, refining	Cultivation, extraction, refining	Pressing and filtration
Availability and circularity	Limited amount of recycled material	Dependent on the forestry industry	Large-scale but environmentally damaging	Limited by cultivation capacity

 

 

Conclusion:

• Recycled rapeseed oil has the lowest climate impact and is the most sustainable choice. It is also the only one based on circularity.

• Tall oil has lower CO2 emissions than newly produced rapeseed oil, but requires chemicals and depends on the forestry industry and thus continued deforestation.

• Soybean oil has the greatest environmental impact.

• Flaxseed oil has a low environmental impact and requires little cultivation area, but often comes from Russia and China; it is also not circular. 

 

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