Focus – Surprise discovery: Grey hair a sign of a defence mechanism against cancer

Grey hair has long been considered an inevitable sign of ageing, a visual reminder of the passing years and the changes that accompany the organism.

But new scientific research is challenging this simple view, showing that silver strands may be a sign of the organism’s defence mechanisms against cancer.

A new study in mice has revealed the remarkable way in which the organism manages cellular damage, a process linked both to ageing and to cancer.

During ageing, cellular damage gradually weakens the functioning of cells. In cancer, meanwhile, damaged and unrepaired cells can cause abnormal growth and the formation of tumours.

The study has highlighted an unexpected link between the loss of hair pigment and mechanisms that can help prevent some dangerous cancers.

At the centre of this discovery are melanocyte stem cells. They are located deep in the hair follicles and serve as a reservoir for melanocytes, the cells that produce the pigment responsible for hair and skin colour.

Under normal conditions, melanocyte stem cells continuously supply new pigment-producing cells through a cyclic regeneration process.

This process involves repeated phases of activity, rest and renewal, in sync with the natural cycles of hair growth and shedding.

This ensures a continuous supply of pigment and, for most of life, preserves hair colour.

However, every day the organism’s cells face damage to DNA, the genetic material located inside cells.

This damage can be caused by ultraviolet radiation, exposure to chemical substances and even by the cells’ own metabolic processes.

Cellular damage contributes both to ageing and to the risk of developing cancer, including melanoma, a type of skin cancer.

The new study shows what happens when melanocyte stem cells, located deep in the supportive environment of the hair follicle, suffer DNA damage, particularly a type of damage known as a DNA double-strand break.

When this happens, melanocyte stem cells can undergo a process called senodifferentiation. In essence, this means that the stem cells mature irreversibly into pigment-producing cells and then disappear from the stem cell reservoir.

As a result, grey hair appears over time.

This protective process is tightly controlled by internal signalling pathways that enable cells to communicate with each other. By removing mature cells from the stem cell population, the organism can prevent the accumulation and possible spread of genetic mutations or DNA changes that could favour the development of cancer.

In a sense, each strand of grey hair can be seen as a form of cellular sacrifice: a cell chooses to depart rather than risk transforming into a malignant cell.

Grey hair, however, is not itself a shield against cancer. It is a consequence of a protective process that eliminates potentially dangerous cells.

Conversely, when control mechanisms fail or are influenced by carcinogenic factors, the opportunity arises for a malignant tumour to develop.

This new understanding may also help explain why the risk of developing cancer increases with age.

It is important, however, to stress the limitations of these findings.

The main part of the evidence comes from experiments carried out in mice. For this reason, further studies in humans are needed to understand whether melanocyte stem cells function in a similar way in the human organism.

Biological differences between species, together with the complexity of lifestyle and genetic factors in humans, mean that the relationship between grey hair and cancer risk is more complex.

Nevertheless, the discoveries open new possibilities for research on cancer and ageing.

The story of grey hair, then, is not linked only to outward appearance or the inevitable passing of time.

It is linked to evolution, adaptation and the constant vigilance of the organism’s defence mechanisms.

Silver strands may be an indicator of a deeper biological process: in the confrontation between ageing and cancer, the organism may sacrifice a pigment-producing cell to protect its wholeness. / a.jor.