Urticaria or hives are common in childhood with about 20% of children developing hives at some point.
Hives are often blamed on allergy to a food but very frequently the hives have nothing to do with allergy or food or food additives.
Chronic urticaria is arbitrarily defined as hives that persist for more than six weeks. Acute urticaria are hives that last less than six weeks.
Hives due to an allergic reaction to a food usually occur virtually as the food is being eaten up to approximately 2 hours after it is eaten. It is usually easy to identify which food has created the reaction and it usually occurs in a child who is known to be allergic (except in infancy where a reaction to a food may be the first indication that the child is atopic).
In contrast, hives occuring many hours after eating are unlikely to be due to an allergic reaction to a food and those hives often come and go for a few days. Hives due to an allergic reaction to a food usually last no more than a few hours to overnight and do not recur unless the offending food is eaten again.
Hives that are not due to an allergic reaction are never, or at least rarely, a threat to the child and are not associated with respiratory or other threatening symptoms.
Acute hives that are not related to an IgE-mediated reaction to a food, medication, insect bite or sting and which recur for several days are rarely due to a food, a hidden food additive or a hidden infection. There is no need to place the child on an elimination diet or investigate for chronic infection. These are older ideas that have not been confirmed by current research but are often recommended by alternative practitioners.
Hives are often associated with "physical" causes especially dermographism and less commonly cold or heat. Dermographism is "welting at the site of pressure" and can be identified by history as "welts in the shape of the scratch marks when the child had been scratching the hives". Dermographism can be elicited on examination by applying linear pressure to the skin by the edge of a tongue depressor. The commonest cause of hives associated with dermographism is a serum-sickness-like reaction to an antibiotic especially one in the Cephalosporin family. However, similar reactions occur with penicillins and virtually any antibiotic. Serum-sickness-like reactions usually occur late in the course of the antibiotic use and can occur up to three or four weeks after finishing the treatment. As a result the antibiotic may not be recognised as the cause of the reaction. These reactions can be associated with hives, sore joints (about 30% of reactions), purple discoloration especially as the hives fade (about 20%) and dermographism (about 20%). Dermographism can also result from a viral illness. The hives do not stop until the dermographism fades.
Dermographic wheal elicited on the back of an infant
Cold urticaria can be demonstrated by applying an ice-cube to the forearm for 5 minutes. The wheal can appear during the application or in the rewarming phase after removing the ice-cube.
Cholinergic urticaria usually occurs as small round hives that occur after exercise or a hot shower, when the body is heated.
Urticaria in children commonly occurs with a viral illness.
Papular urticaria occurs as hives on relationship to insect bites and is common in children in the warm months when their legs, arms and even torso are bare.
Urticaria in childhood usually responds to anti-histamine. The newer non-sedating antihistamines are very effective although the short-acting Benadryl is often used for quick relief since its onset of action is often thought to be faster than the long-acting anti-histamines.
The anti-histamines do not cure the urticaria but provide relief while "nature" cures the hives. If the hives are occuring daily or every second day then a longer-acting anti-histamine should be used daily for three weeks or so with the hope that the process will clear during that time. The anti-histamine can then be stopped to determine if the process is still continuing. If the hives are occuring more intermittently then the anti-histamine can be used intermittently, started at the onset of the hives. The short-acting anti-histamine, Benadryl can be used and gives about 4 hours of relief but it also creates more sleepiness than the newer agents. The newer less-sedating anti-histamines can be used intermittently and in my experience, they start acting quickly enough to be satisfactory.
If the urticaria is unresponsive to anti-histamine or persists longer than six weeks and is poorly responsive to anti-histamine, a laboratory investigation can be done. In children the laboratory investigation is rarely fruitful. When the hives are unresponsive to anti-histamine, treatment becomes more difficult, often requiring more than one agent. This occurs more commonly in adults than children.
