Birth, death, sex, murder, foreign influences, impiety, and certain bodily fluids all bring about miasma, pollution. This pollution can be of the body, soul, household, family, city, or land. The job of the purification [katharmos] of family miasma ultimately fell to the women of the family. Women were the washers of corpses, and the bearers of children. Women themselves were not viewed as harbingers of miasma, on the contrary, whereas semen seems to have been the pollutant that caused miasma during intercourse, there is no evidence of menstrual fluid having properties of miasma. Of course, there is still some debate about this (see comments section of link) in the Hellenic community.
"Never omit to wash your hands before you pour to Zeus and to the other Gods the morning offering of sparkling wine; they will not hear your prayers but spit them back"
Hesiod 'Works and Days'
Special rites of katharmos fell exclusively to women, such as the pinning up of hair during most rituals (women typically wear their hair down in ritual only if in mourning, or in certain orgiastic rites, such as those of Dionysus). Purification could also take the form of dancing, which is often associated with women.
The most common form of katharmos today is the preparation and use of khernips. Khernips is created by adding a smoldering brand, such as lit incense or a leaf of smoking herb to salt water. The khernips is then used to wash the hands of supplicants before a ritual takes place or an offering is made.
I have heard some individuals argue that katharmos is nothing more than good hygiene. While I agree that hygiene is a valuable element of working within a Hellenic worldview I see katharmos as something deeper. Katharmos could be achieved by music, tragic theater (k/catharsis), and dance in addition to the more common act of washing. Even medicine itself is a form of katharmos, something to bear in mind when considering the placebo effect.
Likewise, some people equate miasma with sin. Miasma does indeed seem to be related to primal cultural taboos concerning power and transition, but it is not sin. Sin is "the concept of acts that violate a moral rule" Miasma makes no moral judgment except in the case of murder. Confusion can stem from the idea that murder is the greatest form of miasma and carries the most severe consequences. Wikipedia wrongly states that the miasma of murder can only be purified by the death of the murderer.