Flax (Linum usitatissimum) seed provides a nonabsorbable fiber which has been used as a laxative and has also been used topically to treat various skin conditions. Flaxseed oil contains alpha-linolenic acid (ALA), which is partially converted into the omega-3-fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) in the body. Flaxseed oil increases the ALA content of breastmilk, but does not increase the DHA content. Maternal intake of preformed DHA, primarily derived from seafood or other marine oils, is required to increase breastmilk DHA content. Flaxseed is generally well tolerated in adults, with occasional allergic skin reactions occurring. Very limited data exist on the safety and efficacy of flaxseed oil in nursing mothers or infants. However, supplementation of infant formula with ALA appears to improve the infant's DHA status. Flaxseed used by the nursing mother as a laxative or topical poultice are not expected to adversely affect the breastfed infant. Flaxseed oil can be used during lactation, but is not effective in counteracting a low maternal DHA intake, as in vegetarian or vegan diets. Heating breastmilk to 63.5 degrees C reduces the concentration of linolenic acid by about 22%. Freezing milk at -20 degrees C and thawing more than once decreases linolenic acid concentration by an average of 63%. Dietary supplements do not require extensive pre-marketing approval from the U.S. Food and Drug Administration. Manufacturers are responsible to ensure the safety, but do not need to prove the safety and effectiveness of dietary supplements before they are marketed. Dietary supplements may contain multiple ingredients, and differences are often found between labeled and actual ingredients or their amounts. A manufacturer may contract with an independent organization to verify the quality of a product or its ingredients, but that does not certify the safety or effectiveness of a product. Because of the above issues, clinical testing results on one product may not be applicable to other products. More detailed information about dietary supplements is available elsewhere on the LactMed Web site.