For boars, going grey isn't a big deal -- but red hair, on the other hand, may make them more susceptible to stress, according to a new paper from Spanish researchers.

Ismael Galvan of the Museo Nacional de Ciencias Naturales and his colleagues observed a population of wild boars in Spain and compared how much red fur each boar had to their levels of glutathione, a cellular antioxidant linked to stress. Glutathione, also known as GSH, is able to stabilize unstable molecules like chemically reactive oxygen-containing molecules that can contribute to cell damage and death.

It turns out the boars with the highest levels of the reddish pigment pheomelanin in their hair had lower levels of glutathione in their muscles and also had high levels of oxidative stress.

The association may be stronger than a simple correlation, since the production of pheomelanin consumes GSH.

This suggests that certain colorations may have important consequences for wild boars, Galván said in a statement Thursday. Pheomelanin responsible for chestnut colorations may make animals more susceptible to oxidative damage.

But while in humans, gray hair is thought to happen as a result of oxidative stress, the researchers found that boars with a little silver actually had the lowest levels of oxidative damage.

Far from being a sign of age-related decline, hair graying seems to indicate good condition in wild boars, Galvan said.

Boars aren't the only creatures for whom red hair seems to cause problems; studies in humans have linked higher pheomelanin levels to higher rates of cancer. The pigment isn't all bad, though -- in addition to consuming GSH, the production of pheomelanin also removes a component of GSH called cysteine, which can be toxic at high levels.

Galvan hopes his work will spur further research on pigments throughout the animal kingdom.

Given that all higher vertebrates, including humans, share the same types of melanins in skin, hair and plumage, these results increase our scant current knowledge on the physiological consequences of pigmentation, he said.

SOURCE: Galvan et al. Relationships between Hair Melanization, Glutathione Levels, and Senescence in Wild Boars. Physiological and Biochemical Zoology 85: 332-347, June/Aug. 2012.