What Is the Definition of Biodegradable Soap?

The American Society for Testing and Materials defines biodegradability in soap as the ability to decompose naturally to 90 percent water and carbon dioxide within six months of being used.^1,2

But not everything that suds is soap.

True soap differs greatly from a lot of the sudsy liquids used for washing hands, dishes, and laundry. True soap only needs three ingredients to do its job: Oil (vegetable or animal fat), water, and lye (Potassium hydroxide).³ Soap in this basic form (generally bar soap) is environmentally safe, biodegradable soap, as its natural components break down quite quickly with no adverse effect to the environment.⁴

With any other soaps labeled “biodegradable,” be sure to still avoid any potential harm and dispose of the suds correctly. Biodegradable soap is made to break down in soil, not water, so do your washing, bathing, and cleaning at least 200 feet away from any water sources. Then, simply dig a hole six inches deep to dispose of the soapy water in, so the bacteria in the soil can break it down effectively.

True soap is proven to be highly biodegradable,⁴ so it’s best to stick with simple soaps composed mainly of fats for washing and cleaning needs. From a health perspective, if a soap is biodegradable, it’s probably lacking potentially harmful and polluting chemicals. Biodegradability is a great gauge to not only measure the environmental impact of soap, but its toxicity for humans.

Saponification (Science Stuff Alert)

Saponification is a process that involves the conversion of fat, oil, or lipids,⁴⁴ into soap and alcohol by applying heat in the presence of aqueous alkali (e.g. NaOH).^45,46 Soaps are salts of fatty acids, and fatty acids are monomers of lipids that have long carbon chains (at least 10) e.g. sodium palmitate.⁴⁷ Saponification reactions are generally exothermic and almost totally irreversible.⁴⁸

Saponification can be defined as a “hydration reaction where free hydroxide breaks the ester bonds between the fatty acids and glycerol of a triglyceride,^{49, 50, 51} resulting in free fatty acids and glycerol,”⁵² which are each soluble in aqueous solutions. This process specifically involves the chemical degradation of lipids,⁵³ which are not freely soluble in aqueous solutions. Heat-treated lipid residues are more difficult to remove than non heat-treated residues because of polymerization, which is the process in which small molecules combine to create a polymer. Saponification plays a critical role in cleaning lipids which are present in process areas involving cell growth and cell processing, such as bacterial fermentation and cell disruption process.⁵⁴

Most liquid “soaps” — such body wash, hand soap, dish soap, and laundry detergents — derive their cleansing benefits from mostly synthetic suds-inducing surfactants,⁵ compounds which decrease the surface tension of water. Unlike the humble bar soap, most liquid “soaps” rely on loads of chemicals to generate a cleansing effect.

The general rule of thumb is liquid “soaps” are usually more synthetic than bar soap, and thus have greater environmental implications. Soaps of all kinds become worse for the environment and even human health in proportion to their added chemical fragrances, preservatives, dyes, and cleaning boosters. Many of these chemicals take a long time to break down naturally, if at all, and may pose risks to the human body during use.

Unfortunately, some detergents and “soaps” listed as “biodegradable”⁶ are only so in very exacting lab or industrial conditions, thus requiring astute attention to “plant-derived” ingredients. As always, it’s best to buy eco-friendly products with ingredients that are clear, few, and understandable.

What Is the Carbon Footprint of Soap and Detergent?

Soap contributes a surprising amount of carbon to the atmosphere. According to the European Commission,⁷ various soaps, detergents, and other cleaning supplies emit 200 pounds of carbon dioxide (CO₂) per person into the atmosphere every year. Scientists from the Zurich Institute of Environmental Engineering launched a life cycle assessment study of common household cleaning products,⁸ including soaps and detergents. The study considered every factor of soap’s life cycle, including manufacturing, transport and storage, use, and disposal.

The environmental impacts between bar soap and liquid soap/detergents were shocking, and not in a good way for fans of bottled suds:

• Liquid soap has a carbon footprint 10 times higher than bar soap.
• Liquid soap requires almost 20 times more energy to package than bar soap.
• In a 30 second hand wash, people use .35g of bar soap vs. 2.3g of liquid soap.

That means it takes six times the amount of liquid soap to do the same job as bar soap. That magnification travels all the way up and down the soap’s value chain, meaning six times more raw materials and six times the space needed for transport and storage.

Aside from liquid soap’s carbon footprint, the surfactants, preservatives, dyes, and fragrances in it biodegrade quite stubbornly, whereas bar soap (mostly made from oils) degrades rather quickly.

However, the Swiss study did find bar soap has an environmental footprint twice as high as liquid soap, due to the fact that it is largely derived from plant oils (which are farmed). What is more, it takes more water to wash up with bar soap than liquid soap, and with it the environmental costs of heating and treating wastewater.

But if these plant oils can be sourced ethically and sustainably, it could still be a better option than liquid soap from a land-use perspective. Simply put, agriculture has the potential to heal soil and sequester carbon, whereas mines and refineries do not.

Regardless of the product, the majority of the carbon footprint occurs on the consumer level, not in production. Using soaps and detergents sparingly and efficiently will prove the best prevention to unnecessary greenhouse gas (GHG) emissions.

Conventional soap has a dirty carbon footprint in other ways:

• Soaps made from vegetable-based oils present a problem. Vegetable oils require massive amounts of water, land, and energy to produce. Even more insidious is the common use of palm oil in soaps, which is derived from an extremely extractive process leading to the decimation of thousands of acres of native forests in Southeast Asia.¹¹
• Surfactants, the cleaning agents present in most liquid soaps and detergents, are petroleum-based. Most surfactants eventually biodegrade in aerobic conditions, but aren’t readily degradable in anaerobic conditions,⁹ such as underwater and beneath the ground.
• Most liquid soaps (and many bar soaps) contain preservatives, dyes, and fragrances that negatively impact human health and the environment.
• Detergents are water soluble,⁶ meaning they produce heavy foam which has negative effects on the environment.

A biodegradable soap is a step in the right direction, but there’s more to a truly environmentally friendly soap than that. All-natural, sustainable soaps are as good for humans as they are for the planet, taking into account all inputs and outputs of the products’ life cycle. What is more, they contain none of the potentially harmful chemicals present in conventional soaps, resulting in a healthy earth and healthy skin.

What Types of Eco-Friendly Soaps Are Available, And Why Is Palm Oil Bad?

Eco-friendly soaps and detergents are available in bar, liquid, and powdered forms. When looking for the right product, the old adage “less is more” applies. Look for soap with the fewest ingredients possible, and all of them biodegradable. Keep in mind that some ingredients may sound like dangerous chemicals, though in reality they’re completely safe.

If an ingredient is in doubt, the Environmental Working Group’s Skin Deep ingredient database offers in-depth reviews on soap and detergent ingredients.¹⁰

Whenever possible, buy products that are Certified Organic and Fair Trade, and those that offset carbon emissions from their products.

Eco-Friendly Bar Soap

Bar none (excuse the pun), bar soap is almost unequivocally the most eco-friendly option for cleaning up. Because of its solid composition, relatively low carbon footprint, and often compostable packaging, bar soap has the least amount of processing footprint, fewer ingredients, uses less water in production, and (usually) lasts longer ounce-for-ounce when pitted against liquid detergents.

When choosing bar soap, be sure to check the ingredients list for any of the chemicals mentioned later in this article. Alternatively, purchase locally-made products, which have a much lower carbon footprint. Many of these soaps are of exceptional quality and made with all-natural ingredients, and can be found at local farmers markets and boutiques.

Clean Hands, Dirty Soap: Why Palm Oil Free Products Matter?

If it isn’t clear by now, biodegradability doesn’t promise eco-friendliness. Palm oil, a completely biodegradable product, is one of the most unethical “natural” commodity products on the market.¹¹ Palm oil is found in over half of packaged U.S. products, including many soaps. Palm oil requires destructive clearing of tropical rainforests,¹² which destroys critical habitat for endangered species and devastates indigenous communities. In Malaysia and Indonesia, clearing rain forests to make way for palm plantations emits roughly 500 million tons of carbon dioxide every year, representing 1.4 percent of global net carbon emissions.¹³ Palm oil emitted 25-36 billion tons of carbon dioxide per year from 2000-2015.¹⁴

Avoiding soap and shampoo containing palm oil is an important way to ensure biodegradable cleaning products are not contributing to climate change and environmental injustice.^15,16

Best Biodegradable Liquid Soap

Liquid soap is an essential for washing hands and dishes. Thankfully, plenty of sustainable options exist for environmentally-conscious consumers.

Many big-name brands are looking to get their slice of the eco-friendly detergent and soap pie. Major producers now produce countless plant-based dish soaps, hand soaps, and laundry detergents.

When purchasing liquid soap and detergents, consider purchasing them in pouches, refillable containers, or recycled/compostable material. Buying in bulk is also a great option.

• Environmentally friendly hand and dish soap: From simple castile soap to plant-based liquid soap, there’s an eco-friendly option for every need and occasion. The best eco-friendly liquid soaps naturally kill germs and cut grease while leaving hands moisturized. Look for products that:
  • Contain no parabens, sulfates, phosphates, phthalates, artificial dyes, or fragrance.
  • Use natural moisturizers such as olive oil, aloe vera, and glycerin
  • Are cruelty-free and palm oil-free.

• Soapberries. Soapberries have gained massive popularity in recent years for laundry and personal hygiene. This incredible, lathering berry hails from the Sapindus mukorossi tree. When moistened and rubbed, the berries produce a lather that works remarkably well for cleaning. The secret sauce? Soap berries contain saponins,¹⁷ a natural soap-like substance. Soapberry-based products exist for hand soap, laundry detergent, body wash, and shampoo. Many of the better brands out there are independent, know their supply chains well, and are completely biodegradable.

• Plant-based laundry detergents. Plant-based liquid laundry detergents range between almost 100% and 65% plant-based ingredients.¹⁸ When searching for biodegradable detergents and soaps, be sure to identify any, if any, remaining non plant-based ingredients, as well as what “plant-based” ingredients may actually be potentially harmful (see the above list of ingredients to avoid … many of them are still present in “plant-based” soaps and detergents). Look for descriptions on the label indicating the detergent as:
  • “Phtlathate/synthetic fragrance-free”
  • “Plant-based surfactants”
  • “1,4 Dioxan-free”
  • “Petrochemical-free”
  • “Dye-free”
  • “Phosphate-free”
  • “Glycol-free”
  • “Caustic-free”

Keep in mind some plant-based soaps and detergents still contain chemicals that aren’t easily biodegradable. If there are too many non-biodegradable ingredients or you have doubts, it’s always a good idea to just opt for good ‘ol fashioned natural bar soap.

Still, mostly plant-based liquid soaps and detergents are superior to conventional products, which contain a slew of harmful chemicals and petroleum byproducts. A recent study discovered replacing every United States home’s petroleum-based laundry detergent would save 149,000 barrels of oil every year.¹⁹

Do the Best Organic Soaps Mean They’re Good for Your Skin?

Skin is the largest organ in the body, and absorbs 64 percent of what is put on it.⁵⁵ The average soap product likely contains some form of potentially dangerous compound that could hurt you or the environment.

Absorption of harmful ingredients (such as the following) in conventional soap can lead to a slew of allergic reactions:^20,21

• “Natural” rubber
• Fragrances
• Preservatives
• Dyes
• Metals

The best organic soaps are free from the worst toxins, meaning fewer potentially harmful chemicals will be absorbed into the skin. They have a pH similar to conventional soaps, so the pH drying factor of organic vs. inorganic soap is inconsequential. However, many of the toxins present in average soap are known desiccants.

What Sort of Ingredients Should I Look For When Buying the Best Biodegradable Soap?

One of the key differentiators between eco-friendly soap and their dubious counterparts is the use of saponification over surfactants. Where surfactants artificially create a lathering effect, saponification naturally converts fats and oils into soap. Here’s a list of all-natural, safe ingredients common in eco-friendly, biodegradable bar soap:

• Essential oils
• Animal or vegetable oils
  • For liquid soaps, look for “saponified” before the oil name.
• Aloe Vera
• Sodium/Potassium Olivate (saponified olive oil)
• Sodium chloride (salt)
• Potassium hydroxide (potash)
• Citric acid
• Oats
• Vegetable glycerin
• Peppermint
• Clay
• Turmeric
• Tocopherol (Vitamin E, a preservative)
• Goat’s Milk
• Honey
• Olive Oil
• Cinnamon
• Natural Dye
• Lye

Here’s a list of common soap ingredients to steer clear from… they are horrible for both you and the groundwater:

• Parabens:²² Parabens come in a variety of forms, but all include “paraben” in the name. These are a known endocrine disruptor,²³ tricking the body into thinking that it’s estrogen. They can harm human development, and are toxic to the environment.
• Sodium Lauryl Sulfate/Sodium Dodecyl Sulfate (SLS):²⁴ SLS is a surfactant used to bolster the foaming power of soaps. It has been linked to eye,²⁵ lung, and skin irritation, and may be toxic to internal organs in certain doses. SLS is also linked to endocrine disruption, reproductive issues, and developmental issues. SLS is also toxic to aquatic life.²⁶
• Methylisothiazolinone (MIT) and Methylchloroisothiazolinone (CMIT):^27,28 These preservatives are often put in “natural” soap as an alternative to parabens, so be sure to keep an eye out. Risks associated with MIT and CMIT could include skin and respiratory irritation and neurotoxicity.^29,30 They are both corrosive, toxic, and environmentally hazardous.
• Cocamidopropyl Betaine:³¹ This surfactant helps create suds and regulate the viscosity of liquid soaps. It has been linked to skin reactions, contact dermatitis, and environmental toxicity. Keep in mind Cocamidopropyl Betaine may show up on the ingredients list in a number of names, including CADG, Cocamidopropyl dimethyl glycine, Disodium cocoamphodipropionate, Cocoamphocarboxypropionate, and Cocoamphodiproprionate.
• Sodium laureth sulfate (SLES):³² SLES is a surfactant commonly used in liquid soaps, increasing their lathering effect. SLES has been linked to organ toxicity, and irritation to lungs, eyes, and skin.
  • This ingredient is an ethoxylate, which may introduce 1,4-Dioxane,³³ which is known to harm the eyes, lungs, skin, liver, and kidneys, in addition to being potentially carcinogenic.³⁴
• Benzalkonium chloride:³⁵ This substance is used as a foaming agent and/or preservative. It is a known irritant,³⁶ and may elicit contact allergies at extremely low doses.³⁷ Furthermore, BC has been shown to decrease fertility in mice,³⁸ even when not directly applied.
• Triclosan:³⁹ This chemical is the antibacterial agent found in “antibacterial” soap. It’s been linked to creating antibacterial-resistant germs, prompting the FDA to ban it in 2016, so you’ll likely not run into this ingredient in the store.
• Phtalates:⁴⁰ These are becoming less prevalent in many soaps, but still show evidence of toxicity to humans in high concentrations.⁴¹
• Phosphates:⁴² These chemicals cause algal blooms in waterways, leading to oxygen depletion and eutrophication.
• Fragrance: The ambiguous ingredient “fragrance” is ranked high hazard (8 out of 10) by the Environmental Working Group.⁴³ Many fragrances are known toxins or allergens, cause contact dermatitis, disrupt the endocrine system, can cause respiratory disruption, exacerbates asthma, and can be highly toxic to aquatic life.

Purchasing the Best Natural Soap

The decision to purchase the best natural soap depends on more than the ingredients list. The producer should also adhere to a strict environmental ethos and regard for social justice. This means ethical ingredient and labor sourcing, use of recycled or compostable packaging, and having their carbon footprint erased by using a tree planting offset offered by one of the best carbon offset providers out there. (Individuals can figure their emissions with an ecological footprint calculator.)

Finding the best all-natural, organic, biodegradable soap is an important step in reducing carbon footprint in everyday life. From cradle to grave, soap products contribute a surprising amount of social and environmental detriment, from CO₂ emissions and deforestation to negative impacts on human and ecological health.

Replacing conventional soap with all-natural, biodegradable products may cost a bit more in the short term, but represents an investment in a world where soap doesn’t harm the planet. As a plus, the immediate health and environmental benefits of buying all-natural biodegradable soap is worth every extra penny.