I read somewhere that nursing bras should not be dyed for safety reasons.  Is this bogus?  Or are acid dyes more dangerous to children?

Acid dyes are used in dyeing nylon, silk, and wool; some bras are made of (or decorated with) nylon. Nursing bras are usually made of cotton, however.

Some acid dyes are more dangerous than fiber reactive dyes; some are not. The safest of all dyes, in fact, happen to be acid dyes; they are sold as food dye. See "How can I tie-dye with Kool-aid or food coloring?". These are not always the longest lasting of dyes, but they are exceedingly safe to use.

There are a number of acid dyes which are sufficiently toxic and/or carcinogenic that I would think twice about using them on underclothing, and really would rather that most people not use them at all, due to the dangers of exposure during application. There are so many different acid dyes that it is impossible to say which group is safe, aside from the food coloring dyes. For example, Rhodamine B, also known as acid red #52, is considered to be a probable carcinogen. It's a lovely fluorescent hot pink, but I don't like the idea of its being used without appropriate safety precautions. I feel that it is important to research each individual acid dye for safety before use. It is quite likely that the amount of contamination one could get by wearing a nursing bra dyed with rhodamine B is too small to amount to any hazard, but I still don't like the idea.

I like the nursing bras sold by Decent Exposures; since these are 100% cotton, they are easily dyed with safe fiber reactive dyes, such as Procion MX, Cibacron F, or Drimerene K dye. (For more information on how to create the safest dyed clothing with fiber reactive dye, see the last paragraph of the answer to "Is it safe to tie dye underwear?", from October 12. 2004.)