Why is citric acid in shampoo and conditioner?

A. Citric acid isn't used because of the smell. Fragrances are added for that purpose. It has a two-fold reason for addition. Shampoos usually are at pH 5.5 because at slightly acidic pH the scales on a hair follicle lay flat making the hair feel smooth and look shiny. citric acid is used to adjust the pH down to 5.5 (ish). It is a fairly weak acid which makes the adjustment easier. it also has a small amount of preservative action. citric acid as opposed to any other acid will prevent bacterial growth. (I used to work in the lab for a cosmetics company)

A. The full definition of pH is: "the negative antilog^log of the hydronium ion concentration", but I don't know if that wording is beyond your grade level, Pat. The easy way to look at it is that a pH of 0 is as acidic as you can get, a pH of 14 is as alkaline as you get, and a pH of 7 is neutral.

Depending on what grade you're in, you may or may not have been taught logarithmic scales. In a logarithmic scale you "count the zeroes". So your pH of 5.5 is slightly acidic, but it's less acidic than a pH of 5.0. And in turn, a pH of 5.0 is only one-tenth as acidic as a pH of 4.0, only one-hundredth as acidic as 3.0, only a thousandth as acidic as 2.0, etc. Good luck!

@ Ted Mooney, P.E. RET
First of all...
"The full definition of pH is: 'the negative antilog of the hydronium ion concentration' ".

WRONG!!! Clearly this is a bit "beyond your grade level" but pH=-log[H+](base 10 of course), just negative log, not antilog.

Secondly,
"The easiest way to look at it is that a pH of 0 is as acidic as you can get, a pH of 14 is as alkaline as you get"

ALSO WRONG, I'm guess you don't even know what a logarithm is based on that explanation, extremely acidic solutions can have a negative pH, and similarly extremely alkaline solutions can have pH's above 14, some hair care products used in salons get as high as pH=17.

I appreciate the sentiment trying to help this kid out but check your facts.

Thanks T.J. You're right that pH is the negative log, not the negative antilog; thanks for correcting a silly mind-slip. There are exceptions to every rule but if you google "why do we say pH ranges from 0-14" you'll see why this site, like thousands of others, uses those numbers, especially for children. Kids from 2nd & 3rd grade come to this page, but so do high school seniors, and since I don't know whether Pat is in 2nd grade or senior year, starting with "depending on your grade level" seemed appropriate. But you certainly realize that a P.E. knows what logarithms are, so "beyond your grade level" was a deliberate insult. Ask yourself what motivates you to publicly post that on a page where small children are looking for science fair help? For 23 years now we've worked hard to make this site "... a place of camaraderie ... offering a friendly, welcoming atmosphere ... striving to live aloha". So save your ALL CAP, multiple exclamation point, snide comments for Facebook. Pat and I aren't the only ones in this conversation who still have something to learn. Why would you should teach children anti-social behavior? Regards, Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey

A. Ciaron Murphy answers that question on this page, Christopher. If his response is confusing to you, please rephrase your question in terms of his answer? Thanks!

A. Hi, Sarah. Half of that answer is on this page already. Please try your best to phrase your questions in view of what has already been said so that we don't make things hard for others by going in circles. Thank you.

Regards,

A. Hi, Trina.. Citric-based means based on citric acid , which is an acid in citrus fruits. But chemical formulations are complex. You should probably ask the manufacturer for the MSDS for this product (material safety data sheet) and pass that on to your customer. Good luck.

Regards,