Actress Fay Ripley made headlines yesterday when she said that in future she would happily breastfeed her grandchildren – her own children are currently aged 17 and 21.

The reactions were swift and mixed – some people were shocked, thinking it is physically impossible, while others found the idea distasteful.

But the fact is, grandmothers can breastfeed their grandchildren. If they have previously breastfed, this is known as relactation. If a woman who's never been pregnant starts breastfeeding, this is called induced lactation.

A key paper published in 1956 reported on the experiences of ten grandmothers who 'relacted' for their grandchildren. Significantly, the quality of the milk doesn't seem to be significantly different with relactation either, according to a study published in 1980 in the Journal of Paediatrics – although the women who had never been pregnant but then breastfed ('induced lactation') did not produce colostrum, the first form of milk produced by an expectant mum, which is higher in antibodies.

Relactation is generally possible for mothers who have previously breastfed – however, the longer that gap is, the more difficult it may be. 

As a lactation consultant, most of the parents I support with relactation had a difficult breastfeeding experience, regret having stopped and want to give it another go. I've also supported women who had to interrupt breastfeeding to have treatment for breast cancer. If it's a matter of weeks or months between stopping breastfeeding and starting the process of relactation, the chances of achieving a full milk supply are quite good.

But it is not an easy process. It takes time, patience and commitment. The mother will have to pump or put their baby to the breast at least eight times per 24 hours to stimulate milk production. It may take a number of weeks before the breasts start to make milk again. However, for someone years down the line after they've previously breastfed, it's probably going to take longer – and they may not make as much milk as someone attempting to relactate after, say, a few months.

The World Health Organisation says: 'It is often assumed that the shorter the interval since the woman last breastfed... the more likely she is to relactate. Reports from industrialised countries tend to support this. 

'But several from developing countries indicate that relactation sometimes occurs 15 or 20 years after a woman breastfed her last child, including after the menopause.'

There are many older mothers now in their 40s who are perimenopausal (in the lead up to the menopause) and are breastfeeding, so those intervals might not be as big.

If it's a woman who has not previously breastfed – induced lactation – it's much more difficult. This is most commonly practised by parents who wish to breastfeed an adopted baby or a baby born to a surrogate mother.

So how is it physically possible? In order to breastfeed you need milk-making glandular tissue in the breasts. This tissue develops during puberty but only starts to produce milk in response to hormonal changes that take place during pregnancy and after giving birth.

The most important hormone involved in milk production is prolactin. Women who wish to relactate need to increase their prolactin levels in order to start producing milk again. 

They can do this through regular nipple stimulation – either by pumping, having their baby suckle at the breast or both.

There are, in fact, protocols in place for inducing lactation - the most well-known is the Newman-Goldfarb protocol which involves 'tricking' the body into thinking its pregnant and, in turn, prepares the breasts for milk production. 

The person inducing lactation takes the combination birth control pill to simulate pregnancy and the anti-nausea drug domperidone, which increases the prolactin levels (prescribed on an off-label basis - which means it's not licensed for this use). 

They will also follow a pumping schedule to help stimulate milk production. The Newman-Goldfab protocol recommends starting the process of inducing lactation two to six months before the baby is born or arrives.

If you decide you would like to relactate, it is important at the outset to understand that it might not work: as the Centers for Disease Control and Prevention (the national public health body in the U.S.) advised earlier this year: 'It's important to help mothers set realistic relactation expectations based on their individual circumstances. Relactation can be time-consuming. 

'Success depends partly on parental motivation and dedication to the process, as well as assistance from a skilled lactation support provider. Milk production can start as early as a few days after beginning nipple stimulation, but it may take weeks to months.'

So yes, grandmothers can breastfeed babies but these situations usually occur in developing countries and it's very easy in a western context to be flippant about it. In other scenarios, it could be in the case of a family being affected by a natural disaster, where the mother dies and the family either cannot access or cannot afford infant formula. 

In situations like these, a grandmother breastfeeding a baby might be the difference between that baby living and dying.

• A list of lactation consultants in the UK is available on the Lactation Consultants of Great Britain website, lcgb.org

As told to Julie Cook