Shadows on a mammogram are caused by lotion, perfume, deodorant or powder applied under the arms or on the breasts prior to testing, explains the Office on Women's Health. Women should also notify technicians of breast implants to avoid any false readings or shadows that are misinterpreted.
Breasts are less swollen and tender when women avoid mammogram testing the week before their period, explains the Office on Women's Health. Shadows on the film can produce false negatives or false positives that make it difficult to determine the existence of breast cancer.
The U.S. Preventive Services Task Force recommends a mammogram test every two years for women aged 50 to 74, according to the Office on Women's Health.