What is a Pack Year and How Does it Relate to Me?

Pack Years are a Measure of Lifetime Exposure to Tobacco Toxins

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What is a Pack Year?

Pack year is a term used to describe the number of cigarettes a person has smoked over time.

One pack year equals 20 manufactured cigarettes smoked per day for one year. 

For the purposes of this calculation,  one pack contains 20 cigarettes.

Examples:

Example #1:  Joe smoked 10 cigarettes per day for 10 years. 

1/2 pack (10 cigarettes) per day x 10 years =  5 pack years

Example #2:  Jim smoked 30 cigarettes per day for 26 years.

1 pack (20 cigarettes) per day x 26 years = 26 pack years

10 cigarettes (1/2 pack) per day x 26 years = 13 pack years

26 pack years + 13 pack years = 39 pack years

Example #3:  Joshua smoked 40 cigarettes for 42 years.

2 packs (40 cigarettes) x 42 years = 84 pack years

What about Loose Tobacco?

The calculation for pack years is geared toward standard manufactured cigarettes. What about loose tobacco used for roll your own cigarettes or pipes?

Physicians who use the pack year calculation for their patients are unable to apply the same formula when smokers use loose tobacco. So, a translation was derived by measuring the weight of the tobacco in traditional cigarettes and relating that to loose tobacco.  Approximately 1/2 of an ounce of loose tobacco equals 20 commercial cigarettes.  

The following formula was then developed to gauge pack years for loose tobacco smokers, who usually speak of how much they smoke in terms of ounces per week:

Ounces per week × 2/7 × number of years smoked  =  pack years

There are differences between loose tobacco and regular cigarettes, for instance the lack of filters and differences in tar and nicotine inhaled by the smoker, but doctors feel that these factors haven't consistently been shown to relate to consumption and smoking-related disease.

More critical to ill health is the amount of tobacco used over time (pack years) and this measurement helps in that regard.

Why Pack Years Matter

One measure of lung cancer risk for smokers has to do with how many pack years they smoked. This calculation, along with age and smoking history (current or former smoker with less than 15 years smoke-free) is used to determine whether an individual is eligible to be screened for lung cancer.

There is some debate about the accuracy of using pack years as a risk assessment for lung cancer, however. Researchers contend that a person who smokes a half a pack of cigarettes a day for 40 years (20 pack years) for instance,  is at greater risk for lung cancer than someone who smoked two packs a day for 10 years (also 20 pack years).  The damage to health, generally speaking, is going to be less during the first 10 years of smoking than it is after 40 years of exposure to the carcinogens in cigarettes.

Pack years are also factored in when looking at the risk of smoking-related cardiovascular disease and COPD, though again, it is just one of several factors that are considered.

It is safe to say that pack years are a reasonable measure of overall exposure smokers and former smokers have had to the toxins in cigarettes, but is not the only predictor of smoking-related disease.

If you are interested in calculating your risk for lung cancer, this calculator from the American Association for Thoracic Surgery looks at a number of risk factors.  It can even help never smokers assess their lung cancer risk.

Smoking Cessation Help

If you're a smoker who would like to quit, start with the resources below. 

Developing Strong Quit Muscles

Supplies to Have on Hand When You Quit

Nicotine Withdrawal A - Z

Smoking cessation is a scary thought for most smokers, but push through the fear and get going. There's no time like the present to start building the smoke-free life you've dreamed of.

National Center for Biotechnology Information. National Institutes of Health. British Journal of Cancer. That The Effects of Smoking Should be Measure in Pack-Years: Misconceptions 4. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3405232/. Accessed February 2016.

British Medical Journal. “Pack year” smoking histories: what about patients who use loose tobacco? http://tobaccocontrol.bmj.com/content/14/2/141.long. Accessed February 2016.

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