Fir Shower Steamers, Worked Out in Grams

A shower steamer is a small fizzing tablet that you set on the shower floor, and as the steam reaches it, it scents the stall with whatever you added. The chemistry is a single equation, which is what makes it such a satisfying first project with a bottle of fir needle oil. What follows is the ratio, the dose and the order of work, all worked out on paper.

Fir Needle Essential Oil bottle

Fir Needle Essential Oil

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The fizz, in one line

The tablet is citric acid and sodium bicarbonate (baking soda) pressed together. When water reaches them, one molecule of citric acid reacts with three of bicarbonate to give trisodium citrate, water and carbon dioxide. That gas is the fizz. A technical paper from the citric acid maker Jungbunzlauer adds a useful detail: these powders attract moisture, and damp storage can set the reaction off early, caking the mix and releasing gas.

Two habits follow from that. Use as little liquid as you can when you bind the mix, and make sure the tablets are completely dry before they go in a sealed jar.

Getting the ratio right

Using molar masses (anhydrous citric acid 192.1 g/mol, sodium bicarbonate 84.0 g/mol), each gram of citric acid needs about 1.31 g of bicarbonate to react completely. If your citric acid is the monohydrate form, it is heavier per mole, so check the pack and use a little less bicarbonate.

For six tablets of 25 g each (a 150 g batch) we would weigh out:

The cornstarch share is our own reasoning rather than a published figure, so treat it as a starting point and adjust if the mix feels too dry or too damp.

How much fir oil

For skin, we recommend 0.5% to 2% in a carrier. The Tisserand Institute lists 2% to 4% for bath and wash-off products, and notes that bathwater dilutes the oil further. A shower steamer is a different situation: there is no tub, and the scent drifts through the air you are breathing in a small, steamy room. So we would begin at 1% of the mix, which keeps the fragrance noticeable without being heavy.

Oil sharePer 150 g batchDrops in the batchPer 25 g tablet
0.5%0.75 gabout 16about 3 drops
1%1.5 gabout 33about 5 drops
2%3.0 gabout 65about 11 drops

The drop counts assume the relative density of 0.924 on the Certificate of Analysis we publish for one batch and a rough 20 drops to the milliliter, so a drop is about 0.046 g. Droppers vary, so a small kitchen scale is the better tool.

Making them

  1. Stir the fir oil into the cornstarch in a dry bowl until there are no damp spots. Spreading the oil on the starch first means it never meets acid and base in one clump.
  2. Add the citric acid and bicarbonate and mix until even. Craft and grocery shops carry both powders and the silicone molds; we sell only the fir oil.
  3. Mist with witch hazel or water in tiny bursts, mixing between each, until the mix holds when squeezed. If it starts to fizz in the bowl, it has had too much.
  4. Press firmly into the molds, unmold when firm, and leave the tablets somewhere dry until they feel hard through the middle.
  5. Store in an airtight jar once dry, with the date on the label.

Set a tablet where steam and splash reach it but the shower jet does not, since a direct stream dissolves it in moments. Keep it off the floor you stand on, because oily citrate residue can be slippery, and rinse the floor afterwards.

A few kind words about the room

Fragrance in a small, closed space is worth a moment's thought. In a nationally representative US survey of 1,137 adults by Steinemann, about 27% reported asthma or an asthma-like condition, and nearly two thirds of those people reported at least one adverse health effect from fragranced products in general. It was a survey of self-reported experience with scented products broadly, not a study of fir or of shower steam, but it is a good reason to keep the dose modest and to skip scented tablets altogether if someone in the household has asthma. If that is you, a physician is the person to ask.

The same goes for pets. The ASPCA says short diffuser use in a secured area is not likely to be an issue, and suggests avoiding diffusers around birds and pets with breathing problems; a bird or a cat that follows you into the bathroom is a good reason to ask your veterinarian first. Keep the neat oil and the finished tablets out of children's reach too, since a pressed tablet looks a little like a sweet.

If a tablet smells faint, resist raising the dose. An older oil is the more likely cause, and we suggest using conifer oil within about a year or two of opening, kept capped, cool and dark. For gift ideas see our holiday gifts post, and for the oil's dilution basics our skin and pet guide. If you like your fir in a hotter room, there is a separate set of considerations in scenting a home sauna.

One equation, one ratio and a modest dose of oil: that is all a good fir steamer asks of you, and it makes a very pleasant five minutes of steam.

Fir Needle Essential Oil bottle

Fir Needle Essential Oil

Fir Needle Essential Oil from our own shop, in sizes from 0.5 oz to bulk.

From $10.99

Shop Now →

Sources & Further Reading