Bath bomb

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A picture of different types of bath bomb
LUSH brand bath bombs on display in a shop.

Bath bombs are hard-packed mixture of dry ingredients which effervesces when wet. They are used to add essential oils, scent, bubbles and color to bathwater.

Composition[edit]

Bath bombs' primary ingredients are a weak acid and a bicarbonate base.[1] These are unreactive when dry, but react vigorously when dissolved in water to produce their characteristic fizzing over a period of several minutes. This is an acid-base reaction that involves conversion of citric acid and sodium bicarbonate to sodium citrate and carbon dioxide:

C5H7O5CO2H (aq.) + NaHCO3 (aq.) → C5H7O5CO2Na+(aq.) + H2O(l) + CO2 (g)

There is also a side saponification reaction that produces soap. This involves a reaction between sodium bicarbonate and water, which gives carbonic acid and sodium hydroxide. Sodium hydroxide, in presence of essential oils, undergoes a reaction to give glycerol and fatty acid salts as follows:

HOCO2Na+(aq.) + H2O (l) → HOCO2H (aq.) + NaOH (aq.)
RCO2CH2CH(O2CR′)CH2CO2R″(l) + 3 NaOH (aq.) → HOCH2CH(OH)CH2OH (l) + RCO2Na (aq.) (+ R'CO2Na + R''CO2Na)

The other ingredients in bath bombs can vary considerably. However, most have scented ingredients as well as dye to impart a pleasant fragrance and color to bathwater. Lathering agents, such as sodium lauryl sulfate, are also often added to create bubble foams.

Production[edit]

Bath bombs are generally spherical but can be found in a variety of shapes, such as tablets or lumps. Shops offer a wide range of bombs, but they can also be made at home. A simple DIY method[2] is provided below:

  1. Add ½ cup of citric acid, 1 cup of baking soda and ½ cup of corn starch in a bowl
  2. Mix in food coloring, fragrance, essential oils, and other decorative elements
  3. Tightly pack the mixture into a container
  4. Keep mixture inside the fridge for 4–5 hours, or let it stand overnight

Potential health concerns[edit]

Although bath bombs are well tolerated by many people, some additives such as fragrances and dyes can cause irritation. Common skin irritants and allergens found in bath bombs include limonene, linalool and sodium lauryl sulfate.[3] The main ingredients - citric acid and sodium bicarbonate - are generally not considered as skin irritants when used in bath because of significant dilution in water.

References[edit]

  1. ^ Buddies, Science. "Sudsy Science: Creating Homemade Bath Bombs". Scientific American. Retrieved 2016-12-25. 
  2. ^ "How To Make DIY Lush Bath Bombs - DIY Projects for Teens". diyprojectsforteens.com. Retrieved 2016-12-25. 
  3. ^ Audrain, H.; Kenward, C.; Lovell, C. R.; Green, C.; Ormerod, A. D.; Sansom, J.; Chowdhury, M. M. U.; Cooper, S. M.; Johnston, G. A. (2014-08-01). "Allergy to oxidized limonene and linalool is frequent in the U.K". The British Journal of Dermatology. 171 (2): 292–297. doi:10.1111/bjd.13037. ISSN 1365-2133. PMID 24702129.