Babies, under the age of one, should not be given allergy medications of any sort for many important reasons. The first reason is that an infant must be allowed to correctly develop their immunological responses to the outside world. Secondly there is debate that allergy medications may increase a child's probability of developing more extreme allergies. Thirdly, most children may be harmed because other bodily systems such as their liver and kidneys could be damaged by the infusion of medications. Lastly, allergy medication may cover up other possible dangerous diseases and infections. Giving allergy medication to infants is useless at best and at worst could harm your child's health and development.
When a child is in the first year of life, they go through enormous growth and change. Many of the important building blocks leading to neurological, skeletal, and digestive system growth are occurring at an enormous rate. Immunological responses are 'trained' at this point as well. Many of these systems, because they aren't fully developed are unable to cope with what can be put into their bodies. For example, many children are not able to properly digest complex foods beyond milk until well after the first six months of life.
Giving a child allergy medications to a child during this most critical stage of development is dangerous. Allergy medications block many normal chemicals in a babies body that enable them to fight infection and disease. Because their bodies have not fully adjusted to operating in a world filled with contagions and allergens, it is strongly possible that the blocked chemicals in the body would actually cause a child to become more allergic to outside contagions. Because a child is being shielded from normally safe environmental factors, they will develop a greater sensitivity to it.
Please note that whenever anything is ingested in the body, the kidneys and liver have a job of ridding the body of these unnatural blocking chemicals in the body. In adults and young children, this is not a big issue because they have mostly developed organs that are capable of this task. When an infant is given medication, no matter what it is, it places unnecessary burdens on their young and developing kidneys and liver.
The biggest question I ask anyone who gives allergy medications to newborn children is what is wrong with your kid? Just because your baby constantly has green stuff shooting out of every conduit of their body, doesn't necessarily mean they are having an allergy. Allergy medications simply attempt to cover up an immunological response of the body. People who are diagnosed with herpes, do not take allergy medication, although the inflammation appears to be an allergic reaction of some sort. People with cystic fibrosis do not take allergy medications either. Many dangerous diseases appear in the first couple of life and need to be diagnosed properly early for proper treatment.
Giving allergy medication is a risk to a child's development and may interrupt the diagnosis of other disorders. Allergies are horrible, but there are many other worse things a parent needs to stay vigilant about. Inducing artificial immunoresponse blockers into a newborn isn't one of the best options for a parent. Who the hell gives a newborn allergy medication anyways?