What Does Gas Smell Like

In its natural state, gas is colourless and odourless — which means it has no smell at all. However, for safety reasons, a distinct scent is added to gas used in homes and businesses so that leaks can be detected quickly. In the UK, natural gas is treated with a substance called mercaptan, which gives it a strong, sulphur-like smell, often compared to rotten eggs.

This added smell is deliberately unpleasant and difficult to ignore. It acts as a clear warning sign that gas may be leaking into the air, allowing people to recognise the danger early and take action before it leads to fire, explosion, or carbon monoxide build-up.

Why Gas Has a Rotten Egg Smell

Mercaptan is a harmless chemical that contains sulphur and produces a very strong, instantly recognisable odour. The reason it’s used is simple: it’s detectable by the human nose in even tiny concentrations. While natural gas itself doesn’t pose a risk when confined to sealed pipes or appliances, it becomes highly dangerous when it escapes into the open air.

The rotten egg smell is therefore one of the most important safety features built into the UK gas network. It gives homeowners and tenants a simple way to identify a possible leak — even without specialist equipment.

How to Tell If the Smell Is Gas

The smell of gas is often confused with other household odours, such as drains, compost, or even some cleaning products. However, if the scent is sudden, persistent, and unusual, and especially if it seems stronger near gas appliances, pilot lights, or pipework, it should be treated seriously.

If you notice a smell like rotten eggs and can’t find a logical explanation, it’s best to err on the side of caution. Don’t assume it will go away, and don’t try to cover it up with air fresheners or sprays. A gas leak can build up quickly and become dangerous, even from a small release point.

What to Do If You Smell Gas

If you suspect a gas leak in your home, act immediately. Open all doors and windows to ventilate the space and turn off the gas supply at the meter if it is safe to do so. Avoid using electrical switches, mobile phones, or anything that could cause a spark. Leave the building and call the National Gas Emergency Service on 0800 111 999 from outside or from a safe distance.

It’s important not to wait and see what happens. Even if you’re not entirely sure, it’s better to have it checked by a professional. The emergency service will send out an engineer to assess the situation and make the area safe. There is no charge for this call-out in the UK.

Gas Safety and Routine Maintenance

Recognising the smell of gas is just one part of staying safe. Regular maintenance of boilers, cookers, fires, and gas pipework is essential. All gas appliances should be serviced annually by a registered Gas Safe engineer. These checks help prevent leaks, ensure proper combustion, and reduce the risk of carbon monoxide — a poisonous gas that has no smell at all.

If you live in a rented property, your landlord is legally required to have all gas appliances inspected and provide a copy of the Gas Safety Certificate. If you're a homeowner, the responsibility falls to you.

Can Everyone Detect the Smell of Gas?

While most people can easily recognise the rotten egg smell added to gas, some individuals may have a reduced ability to detect it. This can be due to age, medical conditions, or a condition called anosmia, which affects the sense of smell. People who smoke heavily or have long-term sinus issues may also have a dulled response to odours, including mercaptan.

For this reason, some vulnerable households install gas detectors as an added layer of safety. These small electronic devices monitor the air and trigger an audible alarm if gas is detected, similar to how a smoke alarm works. They are especially useful in homes with elderly residents, young children, or anyone with sensory impairments.

Gas Smell Near Appliances or Pilot Lights

If you notice a faint smell of gas near a cooker, fire, or boiler, it doesn’t always mean there’s a leak — but it should never be ignored. It could be caused by incomplete combustion, a poorly sealed connection, or a small leak in the pipework. Appliances with pilot lights or older flexible gas hoses are more prone to issues over time, especially if they haven’t been serviced regularly.

Even if the smell is intermittent, or only present when the appliance is turned on, it’s still a warning sign. A registered Gas Safe engineer can carry out a thorough inspection and run a pressure test to confirm if there’s a problem.

Why the Smell Might Be Stronger in Certain Conditions

The smell of gas can sometimes be more noticeable in enclosed or poorly ventilated areas — for example, under the stairs, in a cupboard, or around built-in appliances. It may also linger longer in colder weather, where airflow is restricted and windows are closed.

Because gas is heavier than air, it can settle in low-lying areas, especially if the leak is slow and consistent. That’s why it’s important to check meter boxes, basements, and ground-floor pipework if you catch a hint of gas. The smell may not be strong enough to be obvious throughout the house, but it can build up in corners or enclosed spaces over time.

Other Gases and Similar Smells

Sometimes people confuse the smell of gas with other odours in the home. Drains, compost, sulphur-rich water, or even certain cleaning products can give off a similar rotten-egg smell. However, the smell of gas has a sharper, more distinct presence — and it tends to become more noticeable the longer you're exposed to it.

If you're ever unsure, it's safest to treat it as a potential gas issue until it’s been ruled out. Engineers can use handheld detectors to identify the presence of gas accurately, giving you peace of mind.

What Happens When You Report a Smell of Gas

When you call the National Gas Emergency Service, the call handler will ask a series of questions to assess the severity and location of the suspected leak. If they believe there’s any risk to life or property, they’ll dispatch an emergency engineer — often within an hour.

When the engineer arrives, they’ll use specialist equipment to detect gas in the air, check connections and appliances, and isolate the supply if necessary. If a leak is confirmed, they’ll either make it safe or advise on further repairs. This initial emergency response is provided free of charge, although repairs or appliance servicing may be referred to your supplier or a Gas Safe engineer.

Gas Leak Warning Signs and What to Do

The most obvious warning sign of a gas leak is the distinct smell of gas — often described as sulphuric or like rotten eggs. However, there are other signs to be aware of, especially in situations where the smell is faint or not detectable. Hissing sounds near a gas pipe, unusually high gas bills without a change in usage, pilot lights that keep going out, or symptoms like dizziness, nausea, and headaches can all indicate a potential leak. If you experience any of these, open windows and doors immediately to ventilate the area, avoid using any electrical switches or naked flames, and leave the property. From a safe location, call the National Gas Emergency Service on 0800 111 999. Don’t try to find the source of the leak yourself or attempt any repairs — trained professionals will carry out the necessary checks and make the area safe. Acting quickly can prevent a serious incident and protect everyone in the property

Final Word

The smell of gas — strong, sulphuric, and unmistakably unpleasant — is there for a reason. It’s a built-in alarm system that helps prevent serious accidents and saves lives. If you detect it in your home, don’t ignore it. Fresh air, swift action, and a call to the emergency service are the safest and most effective steps you can take. Trust your nose — that smell could be the most important warning you ever receive.