L-ascorbic acid is an antioxidant and an essential vitamin for the synthesis of collagen that is considered important for the youthful appearance of skin. It is a common ingredient of skin creams, but this may be unnecessary and even undesirable as l-ascorbic acid may also act as a pro-oxidant (Halliway & Gutteridge, 2007).
In human hair and skin, there are two types of melanin: eumelanin and pheomelanin. Eumelanin gives hair and skin a dark colour and is usually considered beneficial as an antioxidant and a metal chelator (Felix
Electron paramagnetic resonance (EPR) is a tool which investigates molecular species with unpaired electrons. Free radicals such as hydroxyl radicals, believed to cause cumulative cell damage, are EPR-silent because they are short-lived, but can be detected indirectly using the so-called spin traps. Antioxidants like ascorbic acid are believed to neutralise hydroxyl radicals by transferring unpaired electron onto themselves and then forming non-radical species. Ascorbic acid in aqueous solution is also EPR-silent as its free radical form is also short-lived. Melanins are stable free radicals which give a clear EPR signal. The stability of the free radical means that the free radical is not normally transferred to a water molecule to form a harmful hydroxyl radical.
Ten samples of various browns from honey blonde to dark brown, four samples of red hair and four samples of black hair were taken from human volunteers. Red hen feathers as were also obtained well as black crow feathers.
Locks of hair, of about 3 cm length and 0.7 cm thickness, were tied with white cotton thread and suspended in ascorbic acid solutions of 0.0, 0.1, 1, 10 and 100 mM for 24 hours and then dried. The samples were cut into small pieces, put into an EPR measuring tube and the EPR signal was measured. The same procedure was done for control (untreated hair), except that the samples were left in deionised water for 24 hours.
To obtain the accurate
The EPR signal changed only slightly for black hair and black crow feather samples (Table 1). For brown, red hair and red hen samples, the changes were much more significant (Table 1 and Figure 1). Furthermore, for some of brown and red hair samples, there was a clear change in the amplitude of the EPR signal (Lawson
g Values for different hair colour types and their comparison on treatment with ascorbic acid.
Black | 2.0039 | 2.0039 |
Brown | 2.0044 | 2.0057 |
Red | 2.0051 | 2.0056 |
Red hen feather | 2.0054 | 2.0057 |
The EPR signal of eumelanin-rich samples was not affected much; so, ascorbic acid probably caused little change. In contrast, pheomelanin seems to be strongly affected by ascorbic acid. The signal amplitude increase could be because pheomelanin, in the presence of ascorbic acid, induces the creation of free radicals which are then trapped by pheomelanin. These free radicals may not all be trapped and/or could do damage prior to being trapped (whether by pheomelanin, small portion of eumelanin or ascorbic acid). An alternative explanation is that the brown and red hair samples showed increased EPR signal due to the samples being hydrated. Ascorbic acid would then push the equilibrium away from the fully oxidised and reduced forms to semi-oxidised (free radical) form (d’Ischia