Bubble Bath Day

What the day is

Bubble Bath Day is observed on January 8, sensibly placed in the least appealing week of the northern winter.

Origin and background

The origin of the observance is not documented. The physics is tidy and explains every bubble bath failure.

Soap molecules have two ends that want different things: one end is drawn to water, the other repelled by it. Dropped into water they arrange themselves at the surface with the water-hating ends sticking out, which lowers the surface tension enough that the water can stretch into a film instead of pulling itself into droplets. A bubble wall is then a sandwich: a layer of soap molecules, a thin layer of water, and another layer of soap molecules facing the other way.

Everything that kills foam attacks that water layer. Gravity drains it downward until the film is too thin to hold, which is why bubbles pop from the top of a pile first. Evaporation thins it from both sides, which is why bubbles last longer in humid air. Glycerin, in most commercial bubble baths, holds water in the film and slows both.

Two things destroy it outright. Hard water contains calcium and magnesium that bind to soap and precipitate it as scum, taking the molecules out of circulation, which is why the same product foams beautifully in one house and barely at all in another. Oils break the film directly, so bath oil and bubble bath work against each other, and adding both gets you neither.

One practical caution. Pediatricians routinely advise against bubble baths for young children, particularly girls, because the surfactants irritate the sensitive skin and tissue they sit against in warm water for a long soak.

How to take part

• Add the product under the running tap, since agitation makes the foam.
• Skip the bath oil if you want bubbles. Pick one.
• Run it slightly cooler than feels luxurious. Hot water strips skin and flattens foam faster.
• In a hard water area, use more product or a water softener rather than blaming the brand.
• Keep children's baths plain, and save the bubbles for adults.