Rohto Pharmaceutical's Obagi C Serum Renewal Explained: A New Approach to Boosting Intracellular Vitamin C Uptake and How to Choose Among the Concentrations

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Obagi is a brand that Rohto Pharmaceutical has developed after acquiring the rights to skincare developed by Dr. Zein Obagi of the United States. Dr. Zein Obagi now works on lines such as ZO Skin Health, which is sold exclusively through clinics, and is not directly involved in the development of these products. At one point there were concerns about the trademark, but Rohto Pharmaceutical has formally acquired the related trademark rights in Japan. In the 24 years since the brand's launch, it has generated cumulative sales of more than 120 billion yen, and with its 25th anniversary approaching, the company has decided to completely overhaul its flagship Obagi C Serum series.

Obagi C Serum is a pure vitamin C (ascorbic acid) serum that does not contain quasi-drug active ingredients (such as antibacterial agents). Compared with Rohto's budget-friendly products such as Melano CC, it has long been highly regarded by users who want to apply simple, high-concentration vitamin C over the entire face.

The early versions of Obagi used a powerful solvent called ethoxydiglycol to solubilize the vitamin C, and while this delivered strong results, it also tended to cause significant skin irritation. However, through the development of the Melano CC Premium Essence in 2021 and the previous fourth-generation renewal, the line evolved into a milder, ethoxydiglycol-free formula. This renewal goes a step further, making it a fifth generation equipped with technology that improves the efficiency with which skin cells actually take up vitamin C.

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Vitamin C offers an extremely wide range of skin benefits, including antioxidant action, promoting skin turnover, boosting collagen synthesis, suppressing sebum secretion, and inhibiting melanin synthesis. Tests using Rohto Pharmaceutical's artificial skin model also confirmed that more Ki-67-positive cells (a marker of cell proliferation) and more collagen were observed in the presence of vitamin C.

However, no matter how high a concentration of vitamin C is applied externally, cells cannot take it up without limit. Even as the extracellular concentration of vitamin C rises, uptake into the cells plateaus once a certain level is reached, and the excess goes to waste. Even with a high-concentration serum, you cannot get the full benefit if the cells are unable to make use of it.

To address this problem, Rohto Pharmaceutical focused on an approach that creates an environment in which pigment cells (melanocytes) can more readily take up vitamin C. After screening around 300 candidate materials, the company found that iris root extract, a plant extract, increases the intracellular concentration of vitamin C to approximately 153% (about 1.5 times). When more vitamin C is taken up into the melanocytes that produce melanin, melanin production is significantly suppressed. In this renewal, iris root extract has been newly added to every product in the series: C5, C10, C20, and C25 Serum Neo.

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The main formula changes in this renewal can be summarized in the following three points.

1. Addition of iris root extract: Promotes the uptake of vitamin C into cells.
2. A new vitamin C derivative: The previous 3-O-ethyl ascorbic acid has been replaced with 3-glyceryl ascorbate. This overcomes the weakness of crystallization, which tended to occur at high concentrations, and functions as a penetration technology (Advanced C Control EX) that promotes spreadability on the skin's surface and absorption into the stratum corneum.
3. Addition of penetration enhancers and a review of solvents: A polar solvent (alcohol-like) called dimethyl isosorbide has been newly added to improve penetration efficiency. In addition, the proportion of PG (propylene glycol), which is often viewed with concern for its potential to dissolve cells, has been reduced in favor of the less irritating DPG (dipropylene glycol).

The ingredient composition of each concentration is as follows.

• Differences from the old formula: In the base ingredients, PG has been reduced and DPG increased. The derivative has been switched to 3-glyceryl ascorbate, and dimethyl isosorbide and iris root extract have been added.
• Other ingredients: Moisturizing ingredients and plant extracts such as centella asiatica extract, artichoke leaf extract, yeast extract, serine, grapefruit fruit extract, and betaine carry over from the previous product.

• Ingredient features: In addition to the same base changes as C5 (less PG, more DPG), it contains not only dimethyl isosorbide but also bis-ethoxydiglycol cyclohexane-1,4-dicarboxylate (Neosolue-Aqulio) as a penetration enhancer. A distinctive feature is this doubled reinforcement of penetration-promoting ingredients.

• Ingredient features: The solvent composition is designed with a relatively high proportion of water. To stably dissolve ascorbic acid at a high concentration, the proportion of PG is set somewhat higher than in C5 or C10.

• Ingredient features: Ascorbic acid is listed first on the ingredient list, making this the highest-concentration type (estimated at 25%), with more vitamin C than water. The balance of ethanol and DPG has been adjusted, and ingredients such as the hydrolyzed white mustard seed extract exclusive to C25 are still included. An airtight container is used to prevent deactivation due to the high concentration.

As for glycerin, in C5, C10, and C20 it appears quite far down the full ingredient list, making the formulas close to effectively glycerin-free (only C25 contains a somewhat larger amount). This makes them well suited to people who are concerned about skin problems or visible pores caused by glycerin.

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In terms of texture and feel, the serums become thicker and more moisturizing as the vitamin C concentration increases.

• C5: Absorbs into the skin with an even lighter feel than the previous product, and stickiness has been greatly reduced.
• C10: Slightly thick, but the tingling sensation on application has been reduced, giving it a mild feel.
• C20: Distinctly thick, with strong moisturizing power and a good sense of penetration, leaving the skin with a glossy finish. Because of the high concentration, some people may feel a very slight irritation.
• C25 Neo: The thickest and richest texture in the series. With help from glycerin and emollient ingredients, it feels extremely moisturizing.

In addition, the strong energy-drink-like scent that characterized the previous products has been improved. In C20 and C25 in particular, the distinctive strong smell has been toned down and shifted to a gentle citrus and fruity fragrance, making them easier to use every day.

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The sizes and prices (including tax) of the lineup are as follows.

• C5 Serum (12 ml): 3,300 yen
• C10 Serum (12 ml): 4,400 yen / Large size (26 ml): 7,700 yen
• C20 Serum (15 ml): 8,800 yen
• C25 Serum Neo (12 ml): 11,000 yen

If you want the very best care, C25 Serum Neo is an option, but the recommendation for everyday skincare is Obagi C10 Serum, particularly the large 26 ml size (7,700 yen).

Vitamin C can be consumed wastefully if the extracellular concentration is too high, and in light of the various evidence, a concentration of around 10% is considered the most efficient in terms of cost-effectiveness. Furthermore, with this renewal, iris root extract raises the efficiency of uptake into cells by 1.5 times, so even C10 can be expected to deliver benefits beyond what its previous figures would suggest.

You can choose according to your skin condition and goals, such as C5 Serum if you want gentler care for the whole face or want to keep costs down, or C20 or C25 if you want thorough, intensive care, but it is reasonable to start by trying the most well-balanced option, C10 Serum.