Aoife Hearne: I'm worried about giving formula milk to my baby

Research suggests that breast milk has a favourable influence on the infant's gut and microbiome, which protects against the development of allergies. The majority of research focuses on exclusive breastfeeding for the first six months of life

Aoife Hearne: "In terms of allergies, research from multiple research groups worldwide consistently points to the same fact: the longer you breastfeed, the more beneficial it is for the baby.  Extended breastfeeding has been shown to help reduce the incidence of eczema, asthma, wheezing, and allergic rhinitis."

I'm breastfeeding my five-month-old baby.  Now and again, I give him a formula bottle if my supply is low or if I'm going out for the night. 

A friend recently told me that babies are at greater risk of developing allergies if they are not breastfed exclusively until six months.  I'm worried as allergies run in my family. Could she be right?