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The drink-driving limit in England and Wales is 35 micrograms per 100ml. But what does this mean? And what happens to the alcohol in our body.

When you drink Alcohol, it is absorbed into the blood via the lining of the stomach and then processed by your other organs.  Approximately 20% of the alcohol in your system enters directly into the bloodstream from the stomach, with the the rest of the alcohol being absorbed by the small intestine. About 90% of the alcohol that’s travelling in your blood gets cleaned out by the liver, with the rest being filtered via the kidneys (into urine), through your lungs and sweat.

As the liver can only clear out a certain amount of alcohol per hour, the feeling of drunkenness occurs when alcohol is consumed faster than the liver can break it down.  The speed the liver metabolises alcohol varies from person to person.  Many factors affect it including age, gender, body type, whether it was taken with food, speed of consumption, hydration and genetics – it is simply not possible to second guess how long your liver will take to get rid of the alcohol from your blood. We mention a few other factors to alcohol limits in this blog – How much can I drink until I am over the limit.

If you live in England or Wales, in order to drive legally your breath alcohol level must be below 35 µg/100mL.  This volume may not seem like a lot but you can easily be impaired on a lot less. With the factors that affect your liver process, it is likely a smaller person will need less alcohol to be over the limit compared to a larger person – dependent on their tolerances – but this is not ALWAYS the case…  This is why the ‘counting units’ system to establish an alcohol measurement is totally unreliable.  There is no way to tell how intoxicated you will become using just units.

This is where Breathalyzers come in.   They measure the alcohol content of a breath sample, and display the readings in either a Breath Alcohol measurement (35 µg/100mL or 0.35mg/L) or with the older models, give an interpretation of the Blood Alcohol Content (0.08%BAC for England & Wales).  No counting units or hours – just a measured sample to establish how long it is taking the liver to metabolise that alcohol.