Occasional sadness is an unavoidable part of everyday life. It is a normal emotional response to physical and psychological loss. Everyone is affected differently by external and personal factors that may induce sadness. Sadness is not a mental illness, it is an emotion that may last a few minutes, a few days or surface intermittently for years.

Physical Causes

Physical changes that cause loss of independence, dignity, mobility and brain functioning commonly evoke sadness. These changes commonly occur with chronic illnesses, such as heart disease, diabetes, multiple sclerosis or Alzheimer disease. Hormone fluctuations, such as increased estrogen prior to menstruation and during pregnancy, may also trigger periods of sadness. According to the authors of a January 2009 article in the "Journal of Women's Health," 12.2 percent of women have premenstrual syndrome symptoms that disrupt their lifestyle to some degree.

Psychological Causes

Sadness is a reaction to emotional, intellectual, social and spiritual loss. Common examples of psychological losses include the death of a loved one; loss of status, health, income or faith; and loss of hope for the future for yourself or someone else. A different type of psychological sadness is caused by longing for something that is not possible. These nostalgic memories create a wistful type of sadness, while homesickness causes feelings of sadness and loneliness due to the absence of family and friends.

External Causes

When you meet person who is sad, you probably respond with a sad facial expression and supportive words. When you know people or animals are suffering through no fault of their own -- whether in your own community or in other parts of the world -- you may experience feelings of helplessness, distress and a sense of identification with the victims that leave you with a residual type of sadness.

Personal Causes

Some people are more susceptible to sadness than others are. Older adults experience more intense feelings of sadness in response to distressing situations, according to the authors of an April 2011 article in "Social Cognitive Affective Neuroscience." The authors report increased sensitivity and experience with loss as factors that contribute to this enhanced "sadness reactivity."

Authors of a November 2011 study published in the "Psychology of Aesthetics, Creativity and the Arts" investigated whether music can evoke genuine sadness. Researchers found that participants who selected sad music themselves became genuinely sad as it triggered nostalgic memories. The findings showed that when participants listened to sad music selected by the researcher, they experienced less intense sadness. Researchers further clarified that a participant's level of internal compassion and empathy affected the intensity sadness triggered by both personally selected and researcher-selected music.