Breastfed babies are less likely than bottle-fed infants to suffer from eczema as teenagers, research suggests.
A study found that babies whose mothers took part in a large trial promoting exclusive breastfeeding had a 54% reduced risk of the allergic skin disorder at 16.
The Promotion of Breastfeeding Intervention Trial (Probit) recruited 17,046 mothers and their newborn babies in the Republic of Belarus between June 1996 and December 1997.
Half the maternity hospitals and paediatric clinics involved in the study provided support to encourage breastfeeding modelled on guidelines from the World Health Organisation and United Nations Children's Fund's BFHI.
Children of the supported mothers who were breastfed exclusively for a sustained period from birth were significantly less likely to develop eczema than those whose mothers were not given the extra help.
Lead researcher Dr Carsten Flohr, from King's College London, said: "The WHO recommends between four and six months of exclusive breastfeeding to aid prevention of allergy and associated illnesses.
"Our findings add further weight to the importance of campaigns like the Baby-Friendly Hospital Initiative (BFHI), which is tackling low rates of breastfeeding globally."
Eczema causes skin to become itchy, dry, cracked and sore and affects around one in five children and one in 10 adults in the developed world.
More than 13,000 Belarussian teenagers were examined for the study, published in the journal JAMA Paediatrics.
While breastfeeding appeared to protect against eczema, the study provided no evidence that it reduced the risk of asthma.
Dr Flohr's work was supported by the UK's National Institute for Health Research (NIHR) Biomedical Research Centre at Guy's and St Thomas' NHS Foundation Trust.