How to use essential oils in the bath

Don't drop essential oil straight into bath water. Oil and water don't mix, so the drops float on the surface and reach your skin undiluted. Mix the oil into a carrier oil, a foaming base or a dispersant first. An essential oil education body suggests 5 to 20 drops per tablespoon of base: start at the low end and patch test any new blend.

Quick answer
- Why dilute: essential oils don't dissolve in water. Neat drops float, then cling to skin.
- What to mix them in: a carrier oil, a foaming base or a dispersant such as polysorbate.
- What doesn't carry them: salt, milk or baking soda on their own.
- How many drops: 5 to 20 per tablespoon (15 ml) of base, about 1 to 4%. This comes from an essential oil education body. We found no NHS or government figure.
- Oils to leave out: bay, clove, cinnamon bark, lemongrass and thyme of the thymol type.
- First: patch test the diluted blend, never the neat oil.
- Pregnant, or bathing children: ask your midwife or doctor first, and keep bottles out of children's reach.

Why not add oils straight to the bath?

Essential oils are not water soluble. The Tisserand Institute, an essential oil education body, explains that drops poured into a bath sit on the water as a film and attach to skin as you get in. Warmed by the water and unable to evaporate, they can sting, and it says this seems especially bad with citrus oils.

Skin reactions are the problem reported most. The Institute names a skin reaction as the most common adverse reaction to essential oils, and undiluted oil as its most common cause. A 2012 systematic review of case reports also found skin reactions the most common adverse effect, and a 2016 review found most allergic reactions came from pure oils or high-concentration products.

What can you dilute essential oils in?

Mix the essential oil thoroughly into one of these before it goes near the water:

  • A carrier oil. Any vegetable oil, such as sunflower, olive or coconut. It dilutes the essential oil but doesn't disperse it, so the blend floats and clings to the tub and your skin. Jojoba or fractionated coconut oil feels less greasy. The bath will be slippery, so take care getting in and out.
  • A foaming base. A bath base sold to take added essential oils, used as its maker directs. Or put one tablespoon of shower gel in a small dish and mix the oil in just before the bath. Adding oil to the whole bottle can upset its preservative.
  • A dispersant. An ingredient that carries oil into water, such as polysorbate 20 or polysorbate 80. Follow the supplier's directions. The Tisserand Institute suggests starting at equal parts of oil and polysorbate.

Some common mixers don't do this job. The Institute lists salt, milk, baking soda, glycerin and aloe vera among those that will not safely disperse essential oil: the mixer goes into the water and the oil floats free. Epsom salt is on that list, so see our guide to using Epsom salt in the bath for that salt on its own.

How many drops should you use?

Use 5 to 20 drops of essential oil per tablespoon (about 15 ml) of base, for one bath. That is about 1 to 4%, and the figure comes from the Tisserand Institute. The count covers the whole blend, not each oil in it.

We found no NHS or government figure for a bath, so read this as guidance from an education body, not an official limit. The US National Association for Holistic Aromatherapy (NAHA) gives a similar range for oil blends in general, 1 to 5%.

As general guidance, not a rule, start at 5 drops. The Tisserand Institute also warns that some oils have lower safety maximums of their own, so check the oil you are using.

What about ready-made bath oils?

A ready-made bath oil is scented with essential oils. Made with a carrier oil alone, it floats on the water. Made with polysorbate 80, it spreads through the water instead.

What essential oils bring to a bath is scent: warm water, a room that smells of the oil you chose, a slower end to the day. Our guide to lavender and chamomile in the bath looks at that pairing in detail.

If you buy a ready-made one, follow the pack and read the ingredient list. UK cosmetics law requires fragrance allergens such as linalool and limonene to be named once they pass a set level.

Which oils are advised against in the bath?

NAHA says bay, clove, cinnamon bark, lemongrass and thyme of the thymol type (labelled thyme ct. thymol) should be avoided in baths completely. The Tisserand Institute also names lemongrass, clove and cinnamon bark as more likely to cause skin reactions than other oils. These lists come from essential oil bodies, not regulators.

Take care with these too:

  • Citrus oils pressed from the peel. Bergamot, lemon, lime and bitter orange can react with sunlight on skin. NAHA advises staying out of the sun for at least 24 hours after skin use, and lists bergamot labelled FCF as not reacting this way.
  • Old oils. Oxidation makes tea tree oil a stronger allergen, and the main scent compounds in lavender oil also oxidise in air. Keep bottles tightly closed in a cool, dark place.
  • Any oil on damaged skin. US Poison Control advises against using essential oils on damaged skin.

Allergic reactions are not limited to the oils above. A 2016 review counted nearly 80 essential oils that have caused contact allergy. The EU's Scientific Committee on Consumer Safety lists 28 essential oils and similar extracts as established contact allergens in humans, among them ylang-ylang, clove, jasmine, lavender, peppermint and sandalwood. That is a reason to test first, not a list of oils to avoid. If you do react to an oil, you may need to avoid it from then on.

How do you patch test a blend?

Patch test the diluted blend, never the neat oil. The American Academy of Dermatology's method for testing a new skin product works here:

  1. Mix the blend at the strength you plan to use.
  2. Apply it to a small spot where it won't be rubbed or washed away, such as the underside of your arm or the bend of your elbow.
  3. Leave it on for five minutes, as the Academy advises for anything you would normally wash off, then rinse.
  4. Repeat twice a day for seven to ten days.
  5. If your skin stays free of redness, itching and swelling, go ahead.

If you do react, gently wash the blend off and don't use it again. See a doctor if the reaction is severe.

What if you are pregnant?

Speak to your midwife or doctor before adding essential oils to a bath. We found no national NHS guidance on using them in a bath at home, and the NHS maternity leaflets we read differ on timing, so we don't list any oils as suitable in pregnancy. Keep the bath warm, not hot: our guide to bath time and temperature has more.

What about children?

Leave essential oils out of a child's bath unless a doctor or a qualified practitioner has advised otherwise. NAHA says infants, toddlers and young children are more sensitive to them. For babies, the NHS advises plain water, with no liquid cleansers, in the first month.

Bottles need care as well. US Poison Control warns that some essential oils can be poisonous if swallowed, and says to keep them locked up, out of the sight and reach of children. If you think a child may have swallowed one, the NHS advice is to call 999 or go to A&E. If you're not sure it is harmful, call NHS 111.

SLATE's safety reports assess the blocks for adults, so keep them out of a child's bath. Children should always be supervised in the bath.

How do you run the bath?

To use essential oils in the bath, mix them first and add the blend as the bath finishes filling.

  1. Run the bath warm, not hot, close to body temperature, about 37°C.
  2. In a small dish, mix your drops into one tablespoon of base.
  3. Add the blend once the bath is nearly full, then swirl the water with your hand.
  4. Get in carefully, and keep the water away from your eyes.
  5. Soak for 15 to 20 minutes. If your skin stings or feels irritated, get out and wash it with warm water.
  6. Pat dry, and wipe down the tub so the next person doesn't slip.

Don't bathe when drowsy or after drinking alcohol. If you feel light-headed or too warm, get out slowly: being too hot is one of the causes of fainting listed by the NHS.

Essential oils in SLATE

A SLATE block is scented as it is made, so there is nothing to measure. The CALM block carries lavender and Roman chamomile essential oils at 0.75% each: 1.5% of each 22 g block, or about 0.33 g. QUIET carries frankincense and myrrh, and ROOT carries patchouli and vetiver.

Every block includes polysorbate 80 at 2%, which carries oil into the water so it doesn't sit on the surface or leave a ring. Even so, some people can react to a scent, so patch test any new product.

Not every SLATE scent is an essential oil: some blocks use fragrance oils, and some, including SALT and CLAY, are unscented. Contains essential oils. See each block's ingredient list for allergens. Every block also contains sweet almond oil (tree nut). The System explains how blocks combine in a Grid™.

A Grid™ of essential oil blocks
9 CALM · Lavender and chamomile · Quiet the noise
9 QUIET · Frankincense and myrrh · Go inward
9 ROOT · Patchouli and vetiver · Stay grounded
Build this Grid™ →

Common questions

Can you put essential oils directly in the bath?

No. They don't dissolve in water, so neat drops float on the surface and cling to your skin undiluted. Mix them into a carrier oil, a foaming base or a dispersant first.

How many drops of essential oil do you put in a bath?

The Tisserand Institute, an essential oil education body, suggests 5 to 20 drops per tablespoon of base, for one bath. We found no NHS or government figure. Start at 5.

Can you mix essential oils with Epsom salt?

Salt on its own won't carry them. The Tisserand Institute says the salt dissolves and the oil floats free, even if the salt looked dry when you mixed it. Use a dispersant if you want both in one bath.

Can you mix essential oils with milk?

The Tisserand Institute says no: oil mixed into milk still floats on the bath and reaches skin almost undiluted. Advice varies, so we follow the more cautious line.

Why do essential oils sting in the bath?

Neat oil attaches to skin, often in sensitive areas, and the warm water heats it while stopping it from evaporating. The Tisserand Institute says this can happen with any essential oil, and seems especially bad with citrus oils.

Which essential oils should you not put in the bath?

NAHA names bay, clove, cinnamon bark, lemongrass and thyme of the thymol type. Allergies vary from person to person, so patch test any oil you haven't used before.

Sources

SLATE products are cosmetics for external use only. If you have a skin condition, are pregnant, or have any concerns, check with your doctor before use. Patch-test any new product. Keep out of reach of children. Contains essential oils; see each block's ingredient list for allergens. Every block contains sweet almond oil (tree nut).

SLATE is a soak for the body and mind: small-batch bath blocks of cosmetic-grade ingredients, made in the UK. Build your Grid™

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