The awareness of the benefits of human milk for child health has extended to the general population. Women that cannot produce enough milk for their children increasingly demand breast milk from other mothers. In recent years, we have witnessed a surge in the practice of lactating women selling or donating their milk to women that demand it. This practice has become widespread through social networks and web pages in an uncontrolled manner, facilitated by the lack of legislation regulating this activity.

The Spanish Association of Milk Banks (Asociación Española de Bancos de Leche [AEBLH]) urges us to reflect on this habit and to explain the significant consequences that receiving milk from a different mother in an uncontrolled fashion can have on the health of infants. The practice of providing milk from one mother to children other than their own outside the framework of a milk bank is particularly worrisome, especially when this takes place in neonatal units, given the heightened vulnerability of the recipients (very preterm or ill newborns). In this context, every aspect related to safety and quality is of utmost importance.

Human milk is a biological fluid, and thus carries a risk of transmitting infectious diseases from donor to recipient. The infections reported as transmissible through milk include bacterial, viral, parasite and prion infections.2 Thus, viral diseases caused by HIV, CMV or HTLV, which have a considerable impact on the short- or long-term health of the newborn, can be transmitted through human milk.

Furthermore, milk can be exposed to bacterial contamination during its storage and handling (expression, preservation, storage and transport). Research has shown that there is a higher prevalence of bacterial contamination in breast milk sold over the internet compared to milk given by donors to banks, and also that nearly 10% of it contains some cow's milk added to increase the volume of the milk.3 Last of all, the studies published to date have identified maternal milk as a potential vehicle for contaminants. Uncontrolled milk donation poses hazards to recipients due to the potential exposure to harmful toxic substances (pesticides, mercury, medicines, drugs or herbs).

The European Milk Bank Association (EMBA) and the Human Milk Bank Association of North America (HMBANA) have issued a joint statement warning of the dangers involved in this practice (www.europeanmilkbanking.com). The AEBLH has endorsed this statement (www.aeblh.org).

The World Health Organization, too, has included three records that evince the risk of harm secondary to consumption of contaminated human milk sold through the Internet in its Notify Project (Global Database of adverse events associated with any form of tissue donation; www.notifylibrary.org).

Although there are no laws that regulate the activity of milk banks, these facilities, aware of the importance of guaranteeing the quality and safety of HDM, have developed their own systems to control the process, and some of them have quality management systems with ISO 9001:2008 certification.4 Milk is handled following the control systems used in the food industry to minimise bacterial contamination (hazard analysis and critical control points). Donors are subject to a strict selection and monitoring process, and the donated milk to rigorous quality controls before it is accepted.

The selected donors have an interview with a specially trained health professional, including a lifestyle and health habits questionnaire, and must test negative to the following viral and bacterial infections: HIV, hepatitis B and C virus, HTLV and syphilis.

Milk banks refuse donors that use alcohol, tobacco or any type of abused substances. The use of conventional or herbal medicines with potential adverse effects on newborns is also a contraindication for donation.

Milk received in milk banks is frozen until treatment. At the time of reception, the staff verifies that the milk is stored in an appropriate and intact container, correctly labelled and frozen. Each thawed container is subjected to an initial organoleptic test for colour and aroma. Another quality control is performed later (bacterial culture or measurement of titratable acidity) to discard HDM that is very deteriorated or contaminated.

Adequate milk is subjected to a thermal treatment known as Holder Pasteurisation that destroys all forms of vegetative bacteria, viruses such as HIV, CMV, papillomavirus or Zika virus, and parasites such as Trypanosoma cruzi. After pasteurisation, microbiological testing is performed again, and only milk whose samples are free from bacterial growth is considered fit for use. The pasteurised milk is kept frozen.

The temperature during frozen storage and during Holder Pasteurisation are monitored continuously. If there are any deviations from the ranges considered safe, the donated milk must be discarded. The distribution of milk is performed following procedures that ensure proper cold chain management.

Human milk is always dispensed by prescription. The low availability of HDM justifies prioritising its administration to the newborns known to benefit most from it (very preterm, with very low birth weight, or ill).

To date, we have not heard of any infectious adverse effects derived from the use of pasteurised milk distributed by milk banks. The probability of infection is extremely low, given the double controls performed on one hand in donor selection and on the other with the subsequent pasteurisation of donor products.

When it comes to the toxic products that may contaminate milk, the interview with the mother in which she is asked about her lifestyle habits and health condition, combined with the fact that milk bank recipients usually get milk from various donors, make significant exposure to any toxins highly unlikely (newborns would be exposed to insignificant or low-risk concentrations).

The practice of poorly controlled human milk donation through the Internet or even in hospital settings cannot in any way be considered free of risk for the newborn that receives it and thus must not be accepted.

At present, in the absence of legislation regulating the activity of human milk donation, only human milk banks have controls set up that guarantee the safety of the process. The development of a legal framework could contribute to guaranteeing the safety of human milk donation and facilitate its control.

Last of all, promoting the donation of human milk to established banks would increase the availability of safe HDM for those newborns who, on account of their vulnerability, would benefit most from it.