The researchers devised an "itchometer" that was worn by 24 children, and monitored how much they scratched while they slept.
As scratching increased, said the researchers, the levels of two specific chemicals also rose in the children's bloodstream.
Affliction by eczema leads to dry, scaly skin rashes in children, and the condition may persist into adulthood. Sufferers can be treated with steroid creams, but the mechanisms behind the "eczema itch" have remained complex and poorly understood.
However, the latest research has found evidence that itchy sensations are connected to two specific chemicals found in the blood—"brain-derived neurotrophic factor" (BDNF) and "substance P".
During the study, 24 children, with an average age of 11, were made to wear a wrist monitor that recorded wrist movement during the night. The basic purpose behind the use of the devise was to record when the child scratched in their sleep.
Blood tests from the children showed that the levels of the two chemicals in the bloodstream increased with the increase in scratching in the night.
"As far as we are aware, this is the first report to demonstrate that BDNF and substance P are significantly linked to disease activity, quality of life, as well as the levels of scratching as recorded by the wrist monitor," the BBC quoted Kam-lun Ellis Hon, one of the researchers, as saying.
Dr Colin Holden, the President of the British Association of Dermatologists, also hailed the new findings. "For most eczema sufferers, itching is the worst symptom of the disease. It is known to keep children awake at night, which in turn affects parents and can put pressure on the whole family, and even affect children's performance at school," he said.
"It is by discovering the mechanisms behind the disease and its symptoms that we can develop new therapies that specifically target the root cause of the problem," he added.