▶ Previous Artlcle: 1-1-photodynamic-therapies-for-acne/

 

ALA is a precursor required for the creation of heme of red blood cells, and as such, it has very low allergic or contact dermatitis occurrence rates. When ALA is applied to skin, it transforms into porphyrin inside the skin, and a beam with the wavelength required to activate the porphyrin can lead to destruction of the sebaceous glands.

 

The wavelength of light that most readily reacts with porphyrin is 400nm and this blue wavelength band is referred to as the Soret band. Also the wavelength called Q-band reacts well with porhyrin, although its reaction to porphyrin is weaker than the reaction with the Soret band. A beam with the 400nm wavelength cannot penetrate deeply into the skin, and that is why red light with the 600nm wavelength, which can penetrate deep into the skin, is primarily used for treatment of sebaceous glands using PDT.

 

<The reaction degree of porphyrin by light wavelength>

 

PDT using ALA is the most widely used method with excellent results. However, in order to gain long-term therapeutic effect, it must be applied for more than four hours and this may cause side effects, such as tingling, hyperpigmentation, red spots, dandruff or pustule, after the treatment.

 

Methyl- Aminolaevulinic Acid (MAL)

 

MAL is ALA esters combining methyl with ALA. Thanks to such chemical structure, MAL has greater lipid solubility than ALA, and is therefore well absorbed through pores, where sebum is produced, and has higher coefficient of absorption of medication through skin than ALA. Again, in order to achieve long-term effect, it must be applied for more than four hours. However, because it is impossible to keep the 4-hour application time in actual clinic settings, application is in most cases done for 30~60 minutes. When comparing treatment administered for the same amount of time, there is no big difference in results between MAL and ALA.

 

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Chlorophyll

 

The Chlorophyll used for PDT therapy is usually the ‘chlorophyll a’ extracted from spirulina algae. 

 

The molecular weight of chlorophyll is roughly 893.49 Da, which is greater than in case of ALA or MAL.  Because of its greater molecular weight, it is expected that the coefficient of absorption through skin is lower than that of ALA. The wavelength of light primarily absorbed by chlorophyll is blue (400~480nm) and red (650~690nm).

 

Because chlorophyll itself is a photosensitizer, it can react to light immediately after being absorbed into the skin. Compared to any other photosensitizer, the application time is shorter (for 30-60 minutes) and there is no phototoxic response. Side effects, such as pigmentation, rarely occur. However, when used in clinical trials, its effect is weaker than that of ALA or MAL.