10 factors that affect BAC levels

With all these factors influencing your BAC, you should never rely on counting drinks or using calculators to make an important decision. A BACtrack Breathalyzer compensates for all these factors. By using your breath, it can accurately estimate your BAC and tell you where you stand. Without that, you may as well be picking numbers out of a hat. 

Typically, alcohol concentration is higher in people who are smaller. This means you don’t need many drinks to go over the limit. 

Empty stomach

Drinking on an empty stomach causes the alcohol to be absorbed into your bloodstream quickly.2 If you don’t eat before drinking, it’s likely you’ll get drunk sooner. But, eating a meal won’t stop you from getting drunk or mean you’re safe to drive.

Body fat

Our fat cells hold much less water than muscle. This means alcohol isn’t absorbed and sits in your bloodstream until your liver breaks it down. People with higher levels of body fat can have higher levels of BAC.2

Liver health

Your liver does most of the work breaking down alcohol. Someone with liver disease or liver damage won’t be able to process the alcohol as quickly as people with healthier livers. This means their BAC could be affected.3

Age

As you age, there is a slight decline in how quickly your body processes alcohol. This is because your liver and water content can get smaller as you age. This means alcohol can stay longer in your blood and increase your BAC.2

Sex

People assigned female at birth generally have a higher percentage of body fat, lower levels of water in the body, and less of the enzyme that breaks down alcohol, compared to people assigned male at birth.

Lower levels of this enzyme means alcohol will be broken down more slowly and will remain in the blood for longer.3

Alcohol tolerance

If you don’t have a lot of experience with drinking, your tolerance will be lower. Your body isn’t used to it and as a result, your BAC could be higher.2

Medications

Medication can affect how your body breaks down alcohol. Many medicines need to be broken down by the liver, just like alcohol. If you drink while taking these medications (e.g., contraceptive pills), your liver will be slower at processing alcohol, leading to a higher BAC. If you’re taking any medications talk to your doctor or pharmacist about whether you can drink alcohol.

Strength of drinks

Not all drinks have the same amount of alcohol in them. The higher the amount of alcohol, the higher your BAC is likely to be. Check out our page on Standard Drinks for more info.

Why does my BAC matter?

Even very small amounts of alcohol can affect your concentration, judgement, and performance. You may feel like you’re ok, but your reaction times will be slower than normal, and your concentration will be reduced.1

This makes it difficult to perform activities that require skill and concentration, or where the safety of others is involved. For example, driving, flying, water sports, skiing, using complex or heavy machinery, or farm machinery.

Drinking and driving

In Australia, it’s illegal to drive if your blood alcohol level is over 0.05%. 

If you choose to drink, consider different transport options - public transport, rideshare or organising a friend to be a designated driver. 

You must have a 0.00% BAC in most Australian states or territories if you are a:

• learner, provisional, or probationary driver – regardless of age
• truck driver
• bus driver
• driving instructor or if you are supervising a learner driver
• convicted of driving under the influence (DUI).

Even if you’re below 0.05% BAC, your judgement, reaction times and driving skills are impacted. 

A BAC 0.05% and above significantly increases the risk of car crash and fatality.4

Drinking and working

Blood alcohol limits apply in jobs like flying planes (e.g. no alcohol within 24 hours of flying), driving public or heavy vehicles, operating commercial ships or machinery. In these jobs, the BAC limit is zero (0.00%). If you’re unsure what your employer’s required BAC limit is, make sure you find out before getting behind the wheel. 

Some workplaces implement alcohol and drug testing as a protocol. You can be tested as part of pre-employment screening, at random or following an incident in the workplace.

Workplaces usually only enforce alcohol testing when they are legally obligated to, or where employers, workers and unions agree it’s necessary.

Make sure to read your employment agreement and company policies to check what your obligations and rights are.

How is BAC measured?

Blood alcohol concentration can be measured with a breathalyser, or by analysing a sample of blood, saliva, or urine.

Driver testing

The police do breathalyser tests at random breath testing (RBT) roadblocks, or if they think you might be drink driving.

If you blow 0.05% or over, they’ll need to do a second test at a police station. If your second result is over the legal limit, you can be charged with driving under the influence (DUI).

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