What is Red No. 40?

Medically Reviewed by Poonam Sachdev on June 27, 2022
Written by Alyssa Anderson
5 min read

Red no. 40 is a synthetic dye that’s used in a variety of foods. It’s one of nine synthetic dyes that the U.S. Food and Drug Administration (FDA) has approved for human consumption. It’s also currently approved by the European Food and Safety Authority (EFSA). 

The full name of this dye is FD and C red no. 40. It’s considered a color additive. This describes any substance that adds color to food, cosmetics, and drugs. 

Red no. 40 consists of a chemical compound called Allura red AC. This is a naphthalene sulfonic acid. 

Allura red AC typically comes in the form of a dark red powder or small granules. You can dissolve it in water, 50-percent-alcohol solutions, glycerol, and propylene glycol. 

When it’s heated to extreme temperatures — to the point where it molecularly decomposes — it emits toxic fumes composed of nitrogen and sulfur oxides. Luckily, you should never reach such extreme temperatures when using this substance in food production.   

There are also non-colored components of the dye. These are typically sodium chloride and sodium sulfate. 

Red no. 40 is a synthetic food dye. This means that it doesn’t occur anywhere in nature and needs to be created through man-made processes. 

Specifically, it’s the product of a chemical reaction that involves two different types of sulphonic acids. This reaction couples a type of toluene sulphonic acid with a different type of naphthalene sulphonic acid. 

There are a number of products that stem from this reaction. Allura red AC is associated with the sodium salt that's produced. Calcium and potassium salts are also created and are considered safe components of the reaction. 

Over 30 companies currently produce this dye.

The purpose of red no. 40 — and all synthetic dyes — is to create distinct, uniform colors in consumable products. They’re great for fun, eye-catching foods like cake mixes, frostings, and soft drinks. They’re commonly added by large-scale food manufacturers but can also be used in home cooking. 

Color additives can also help consumers identify the flavors of consumable goods. For example, purple coloring usually implies a grape flavor, and yellow usually implies lemon. Using red no. 40 could imply some kind of cherry, strawberry, or raspberry flavor. Synthetic dyes can blend together easily, which allows you to get a wide variety of hues. 

The FDA has to approve every type of dye before it can be used in consumable goods. Synthetic dyes need to go through the approval process for every new use. The FDA specifies exactly how the dyes can be used and the amount that’s allowed. 

Red no. 40 is approved to add color to a wide range of food products. These include: 

  • Gelatins
  • Puddings
  • Beverages — both alcoholic and non-alcoholic
  • Dairy products
  • Frostings
  • Fruits
  • Bakery products
  • Jams
  • Condiments
  • Meat and poultry 

Allura red AC can also be used to color arts and crafts supplies like crayons, pens, and markers.

The FDA has ruled that red no. 40 is safe for public consumption. They reviewed the dye as recently as 2019. 

There’s some controversy about the ruling that this dye is completely safe, though. People are petitioning the FDA to at least include a warning label in all foods that contain this synthetic dye.  

The reason for this protest is that preliminary evidence indicates that consuming certain synthetic dyes might make symptoms of attention deficit hyper activity disorder (ADHD) worse. The synthetic dyes that could be to blame include: 

To date, studies have only shown very minor effects from these dyes. There are also some problems with most of these studies, calling into question the quality of the data. Problems include things like studying so many additives at one time that it’s impossible to pin the effects on a particular substance. 

However, overall, there does seem to be conclusive evidence that consuming certain synthetic dyes, like red no. 40, can increase hyperactivity — and possibly irritability — in susceptible children. Only a small percentage of people are affected. Most of these people are children who are diagnosed with ADHD and seem to be particularly sensitive to these additives. 

To be clear, there’s no evidence that consuming these dyes actually causes ADHD, but they might make certain symptoms worse. 

The FDA, however, needs more evidence before they’re willing to add a warning label to foods that contain red no. 40. 

Despite their relative safety, some families may want to avoid synthetic dyes. This is particularly likely if you believe that your child is sensitive to food dyes. 

There are a few tips that you should keep in mind to help you with this process. 

  • Carefully read food labels to see if particular synthetic dyes are listed.
  • Avoid processed foods.
  • Carefully research fast food places before making any purchases — many include synthetic dyes in ways that you wouldn’t necessarily anticipate.
  • Stick to fresh foods like fruits and vegetables at snack time.

You can try eliminating all foods with synthetic dyes from your child’s diet for at least two weeks to see if they’re particularly sensitive. You should carefully observe and record their behavior, though, for two weeks prior to this trial period. Continue doing this throughout the trial period to see if eliminating synthetic dyes affects their behavior in any way. 

Synthetic dyes are regulated in a very specific way by the FDA. Manufacturers have to undergo a process called batch certification. This means that the FDA needs to test a subset of samples from every new batch that a company produces. 

This is different from how they regulate natural dyes. Naturally occurring dyes need to be approved for use in food once. Then, they can be used as needed. 

There are a number of factors that the FDA considers when evaluating a synthetic dye either for first-time approval or for a new use. These considerations include: 

  • Short and long-term effects of consuming the dye
  • The composition of the substance
  • Its properties
  • Its stability
  • The likely amount that people will consume or otherwise encounter
  • The quality and availability of analytical methods needed to determine the purity and amount of the dye

Like all synthetic dyes, red no. 40 needs to be listed by name on food labels.