Just breathing in cigarette smoke regularly is enough to lead to breast cancer, especially in premenopausal women. The danger level is comparable to that of active smoking. 
“It is time to strengthen the restrictions on cigarette smoke in all environments,” Dr. Kenneth C. Johnson from the Canadian Public Health Agency stated.
Johnson investigated the relationship between the risk of breast cancer and smoking (both passive and active) by analyzing 19 previously published studies. The results indicated that regular passive smoking over a long duration increases the risk of breast cancer by an average of 27% among women who have never smoked. In some studies, this risk even rose to 80-90%.
In 14 studies, “the relationship between passive smoking and the risk of cancer during the premenopausal period is very clear, with an increase of 68% in those who are frequently and long-term exposed to cigarette smoke, despite never having touched a cigarette in their lifetime.” This risk could be as high as 119% in the remaining 5 reports.
Compared to women who have never inhaled cigarette smoke, those who actively smoke have a 46% increased risk, which can even reach 108% in certain studies.
Mỹ Linh (according to Reuters)
