Danger, Warning, Caution: what the signal word on a label is telling you

Turn almost any cleaning product around and, somewhere near the top of the back label, there is one word in capital letters standing on its own. Danger. Warning. Sometimes Caution. It is the shortest line on the label and, for a quick decision about where a bottle should live, often the most useful one.

The catch is that the word does not mean exactly the same thing everywhere. A European label, an American household cleaner and an American insect spray each follow a different rulebook, and the three rulebooks use the words a little differently. This piece goes through each one and then reads two sample labels line by line, the way I would if they were on the counter in front of me.

Three rulebooks at a glance

The rest of this piece is really just those three rows, opened up.

Under GHS and CLP: two words only

The Globally Harmonized System, which sits behind European labels and US workplace labels, uses just two signal words. OSHA's Hazard Communication Standard puts it plainly: "Danger" is used for the more severe hazards and "Warning" for the less severe. There is no Caution in this system.

The word is not chosen by feel. Each hazard class and category comes with its own signal word, set out in the rules. A few examples from the tables show the pattern:

• A product that causes severe skin burns and eye damage gets Danger, with the corrosion pictogram.
• A product that causes skin irritation gets Warning, with the exclamation mark.
• A liquid classed as extremely or highly flammable gets Danger. One classed simply as "Flammable liquid and vapour" gets Warning. Both carry the flame.

The EU's CLP Regulation adds a tidy rule: where Danger appears on a label, Warning must not appear as well. So even a product with several hazards shows one signal word, the one for its most serious hazard. If you see Danger, the label is telling you that at least one thing about the product sits at the severe end.

Two more details are worth knowing. Some lower-level hazard categories carry a signal word with no pictogram at all, so a lone "Warning" without a red diamond is not a printing mistake. And some products carry no signal word because they are not classified as hazardous. That is a classification result, not a promise that the product is harmless. If you want the pictograms that usually stand next to the word, our guide to the nine hazard pictograms takes them one at a time.

On US household products: Danger, Warning or Caution

Cleaners, polishes, solvents and similar products sold for household use in the US are covered by the Federal Hazardous Substances Act, which the Consumer Product Safety Commission administers. Its labelling list sits in the federal regulations at 16 CFR 1500.3, and it is worth a look because it is short and practical.

A hazardous household product must carry, among other things:

• the signal word "DANGER" if it is extremely flammable, corrosive or highly toxic;
• the signal word "WARNING" or "CAUTION" for all other hazardous substances;
• a plain statement of the main hazard, such as "Flammable", "Vapor Harmful" or "Causes Burns";
• the word "Poison" for anything defined as highly toxic;
• precautionary measures, and storage and handling instructions where special care is needed;
• the statement "Keep out of the reach of children" or its practical equivalent;
• the name and place of business of the maker, packer, distributor or seller.

Notice the "or" in the second line. Under this law, Warning and Caution sit on the same step. A household cleaner marked Caution is not meant to be read as gentler than one marked Warning. Both say the product is hazardous but below the Danger level.

On US pesticides: a three-step ladder

Pesticides are different, and the word "pesticide" covers more than people expect. In the US, products that claim to kill germs on surfaces are regulated by the Environmental Protection Agency as antimicrobial pesticides, alongside insect sprays, ant baits, weedkillers and rodent baits. Their labels follow EPA rules, and here the three words do form a ladder.

EPA's Label Review Manual sets it out by toxicity category:

On top of that, products in category I for acute oral, dermal or inhalation toxicity must also carry the word POISON, printed in red, together with the skull and crossbones, close to the word DANGER.

Placement is set out too. The signal word goes on the front panel in capital letters, on its own line, close to the statement "Keep Out of Reach of Children", which almost every pesticide label must carry. EPA's guidance also tries to keep the three words from turning up elsewhere on a pesticide label as ordinary language, so they cannot be confused with the signal word.

So on a US pesticide, Caution really does rank below Warning. On a US household cleaner, it does not. That small difference is the main reason the same word can feel slippery.

Label one: a European limescale remover

Here is a sample label of the kind you might find on a strong bathroom descaler bought in Europe. The product is made up, but the wording follows the CLP pattern.

1. The pictogram: one red diamond, corrosion. That already tells me the type of hazard.
2. The signal word: Danger. That tells me where it ranks: the severe end.
3. The hazard statement: "Causes severe skin burns and eye damage." This is the reason for the Danger.
4. The precautionary statements: keep out of reach of children. Wear protective gloves and eye protection. Store locked up. These are the instructions I actually act on.
5. The supplier's name, address and telephone number, required on every CLP hazard label, and useful if I need to find out more about the product later.

What I do with it: top shelf or a locked box, gloves and eye protection on before the cap comes off, one product at a time in the bathroom, window open, and the bottle goes back to its shelf as soon as I am done. There is no Warning anywhere on the label, which fits the CLP rule. The Danger covers it.

Label two: a US insect spray for indoor use

Now a sample of a typical US ant and roach spray, again made up but following the EPA layout.

1. "KEEP OUT OF REACH OF CHILDREN" on the front panel.
2. "CAUTION" directly below it. On a pesticide, that puts the product in toxicity category III, or category IV where the maker chose to use the word anyway.
3. An EPA registration number: a short number with dashes. It identifies the product and tells me this is a pesticide label, so the EPA ladder applies.
4. "Precautionary Statements: Hazards to Humans and Domestic Animals", with the signal word repeated and a few lines such as avoiding contact with skin or eyes and washing hands after use.
5. "Directions for Use", which on a pesticide label are not suggestions. EPA states that it is a violation of federal law to use the product in a way that does not match its labeling.

What I do with it: Caution on a pesticide is the lowest step, but it is still a step. The can goes high and closed, away from the cooker and heaters if it is an aerosol, and the spray goes only where the label says, with children and pets kept out of the room as the directions ask.

Put those two labels side by side and the lesson is clear. Danger on the descaler and Caution on the insect spray are not on the same scale, but each word is honest within its own rulebook. Read the word first, then check which rulebook you are in.

What the signal word cannot tell you

The signal word ranks how severe the worst hazard is. It does not tell you what kind of hazard it is (the pictogram and hazard statement do that), and it does not tell you what to do (the precautionary statements do that). A bottle marked Warning for flammability and a bottle marked Warning for skin irritation need very different storage.

It also says nothing about children's curiosity. Every product in the cupboard, whatever its word, belongs out of reach. Our Reading Labels section covers the other parts of the label in turn.

If someone has been exposed

If someone may have swallowed a product, breathed in its fumes, or splashed it on their skin or in their eyes, call your local emergency number or a poison center now, with the product or its label in your hand. In the US, Poison Help is 1-800-222-1222. In the UK, call NHS 111, or 999 in an emergency. In the EU, call 112. If the person is unconscious, having trouble breathing or having a seizure, call 911, 999 or 112 straight away. More contacts are on our official help page.

When you call, read out the product name and the signal word, then the rest of the label as you are asked. That one capital-letter word is usually the first thing the person on the line will want to hear.