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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Hydroquinone
Brand Name
Obagi C Rx System C Clarifying Serum
Generic Name
Hydroquinone
Active Ingredient
HydroquinoneCategory
Melanin Synthesis Inhibitor [EPC]
Variants
1
Different strengths and dosage forms
| Strength | Form | Route | NDC |
|---|---|---|---|
| 40 mg/mL | SOLUTION | TOPICAL | 62032-106 |
Detailed information about Obagi C Rx System C Clarifying Serum
This page is for informational purposes only and does not replace medical advice. Before using any prescription or over-the-counter medication for Obagi C Rx System C Clarifying Serum, you must consult a qualified healthcare professional.
Hydroquinone is a potent melanin synthesis inhibitor used topically to treat hyperpigmentation. It works by inhibiting the tyrosinase enzyme, effectively lightening dark patches of skin such as melasma and age spots.
For the treatment of hyperpigmentation in adults, the standard application involves a thin layer of Hydroquinone (2% or 4%) applied to the affected area twice daily—once in the morning and once in the evening.
Hydroquinone is generally not recommended for use in children under the age of 12. Safety and efficacy data for the pediatric population are extremely limited. In rare cases where a teenager requires treatment for severe post-inflammatory hyperpigmentation, a healthcare provider must supervise the treatment closely. Pediatric skin is often thinner and more permeable, increasing the risk of systemic absorption and localized irritation.
Because Hydroquinone is excreted renally after systemic absorption, theoretically, patients with severe renal failure should be monitored. However, because systemic levels from topical application are typically low, standard dose adjustments are rarely required. Caution is advised if applying to very large surface areas.
There are no specific guidelines for dosage adjustment in hepatic impairment. However, as the liver is responsible for the conjugation of absorbed Hydroquinone, patients with end-stage liver disease should use the product sparingly and avoid application to broken skin.
Elderly patients often have thinner skin (atrophy). Healthcare providers may recommend once-daily application initially to assess tolerance and prevent severe irritation or skin tearing.
If you miss a dose, apply it as soon as you remember. However, if it is almost time for your next scheduled application, skip the missed dose and return to your regular routine. Do not apply a double amount to 'make up' for the missed dose, as this significantly increases the risk of chemical irritation.
Acute systemic overdose from topical application is virtually impossible. However, 'chronic overdose' (using too much for too long) can lead to exogenous ochronosis. If the product is accidentally ingested, symptoms may include tremors, seizures, and hemolytic anemia. In the event of ingestion, contact a Poison Control Center or seek emergency medical attention immediately.
> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your dose or extend the length of treatment without medical guidance. Prolonged use beyond 6 months without a 'drug holiday' is generally discouraged by dermatologists.
Most patients using Hydroquinone will experience some degree of localized skin reaction. These are generally mild and expected as the skin adjusts to the medication:
> Warning: Stop taking Hydroquinone and call your doctor immediately if you experience any of these serious reactions:
With prolonged use (typically over 6 months of continuous daily application), the risk of permanent skin changes increases. The most concerning long-term effect is the aforementioned Exogenous Ochronosis. Once this condition develops, it is extremely difficult to treat and may be permanent. Additionally, long-term use can lead to 'confetti-like' depigmentation, where small white spots appear within the treated area, creating an uneven skin tone. To prevent these effects, most clinical protocols suggest a '3 months on, 1 month off' cycle.
There are currently no FDA black box warnings for Hydroquinone. However, the FDA has issued significant safety communications regarding the potential for ochronosis and the lack of safety data for long-term OTC use, which led to the 2020 reclassification of the drug to prescription-only status.
Report any unusual symptoms or changes in skin color to your healthcare provider immediately. Early detection of adverse reactions is key to preventing permanent skin damage.
Hydroquinone is a potent chemical agent that must be handled with care. It is intended for external, topical use only. It should never be ingested or applied to mucous membranes (inside the nose, mouth, or genital area). Because Hydroquinone reduces the skin's natural protection against the sun (melanin), users are at a significantly increased risk of sunburn and long-term UV-induced skin damage. Strict adherence to sun protection measures is the most important aspect of Hydroquinone safety.
No FDA black box warnings for Hydroquinone have been issued as of 2026. However, its use is strictly regulated due to the risk of ochronosis and the potential for skin sensitization.
While systemic lab tests (like blood counts) are not typically required for topical Hydroquinone use, regular clinical skin assessments are essential. Your healthcare provider should examine the treated area every 2 to 3 months to:
Topical Hydroquinone does not cross the blood-brain barrier in significant quantities and has no known effect on the central nervous system. It is considered safe to drive or operate machinery while using this medication.
There are no known direct interactions between topical Hydroquinone and moderate alcohol consumption. However, alcohol can cause vasodilation (widening of blood vessels), which might temporarily increase the redness or 'flushing' sensation in skin already irritated by Hydroquinone.
Hydroquinone does not require a complex tapering schedule to avoid systemic withdrawal. However, 'rebound hyperpigmentation' can occur if the drug is stopped suddenly without maintaining strict sun protection. Dermatologists often recommend transitioning to milder brightening agents (like Azelaic acid or Vitamin C) when discontinuing Hydroquinone to stabilize the melanocytes.
> Important: Discuss all your medical conditions, especially asthma or sulfite allergies, with your healthcare provider before starting Hydroquinone.
There are no documented interactions between topical Hydroquinone and specific foods. Unlike some oral medications, Hydroquinone's efficacy is not affected by diet. However, maintaining a diet high in antioxidants may theoretically support skin health during the depigmentation process.
Hydroquinone is a reducing agent. If systemically absorbed in large amounts (which is rare), it could potentially interfere with certain urine glucose tests that rely on copper reduction methods (like Clinitest), leading to false-positive results. It does not typically affect standard blood chemistry or hematology panels.
For each major interaction, the primary mechanism is usually pharmacodynamic (additive irritation) or physical (chemical staining). Management involves spacing the application of different products or using them on alternating days.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, including any other skin creams or 'brightening' serums you purchased without a prescription.
Hydroquinone must NEVER be used in the following circumstances:
Conditions requiring a careful risk-benefit analysis by a physician include:
There is a potential for cross-sensitivity between Hydroquinone and other phenolic compounds (such as resorcinol or phenol). Additionally, patients who are sensitive to 'sulfa' drugs should not confuse them with 'sulfites'; however, any history of chemical sensitivity should be disclosed to the prescribing physician.
> Important: Your healthcare provider will evaluate your complete medical history and skin type before prescribing Hydroquinone. Do not use a product prescribed for someone else.
Topical Hydroquinone is absorbed systemically in significant amounts (up to 45%). While there are no well-controlled studies in pregnant women, the high absorption rate makes it a drug of concern. Most dermatologists and the American College of Obstetricians and Gynecologists (ACOG) recommend avoiding Hydroquinone during pregnancy unless the potential benefit clearly outweighs the risk. Melasma during pregnancy (chloasma) often resolves spontaneously after delivery, making the risk of medication use unnecessary in most cases.
It is not known whether topically applied Hydroquinone is excreted in human milk. Because many drugs are excreted in milk and the systemic absorption of Hydroquinone is relatively high for a topical, caution should be exercised. If used, it should not be applied to the breast area to prevent the infant from accidentally ingesting the cream or coming into direct skin-to-skin contact with the treated area.
Safety and effectiveness in pediatric patients below the age of 12 have not been established. Use in children is generally discouraged due to the risk of systemic absorption and the lack of clinical trials in this age group.
Clinical studies of Hydroquinone did not include sufficient numbers of subjects aged 65 and over to determine if they respond differently than younger subjects. In general, dose selection for an elderly patient should be cautious, starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy. Older patients may also have thinner skin, which increases the risk of irritation.
No specific GFR-based (Glomerular Filtration Rate) dose adjustments are provided by manufacturers. However, since the metabolites are cleared by the kidneys, patients with end-stage renal disease (ESRD) should be monitored for signs of systemic toxicity if using the drug over large surface areas for extended periods.
No specific adjustments are required for mild to moderate hepatic impairment. In cases of severe liver failure, the body's ability to conjugate and neutralize absorbed Hydroquinone may be reduced. Use should be limited to the smallest effective area.
> Important: Special populations require individualized medical assessment. Pregnant or nursing women should always consult their obstetrician before using any medicated skin products.
Hydroquinone is a dihydric phenol that acts as a potent melanogenesis inhibitor. Its primary molecular target is the enzyme tyrosinase. Tyrosinase is responsible for the first two steps of melanin synthesis: the hydroxylation of tyrosine to DOPA and the subsequent oxidation of DOPA to dopaquinone. Hydroquinone acts as a 'false substrate,' binding to the enzyme's active copper-containing sites more effectively than tyrosine itself.
Furthermore, Hydroquinone affects the melanocyte's internal structure. It increases the degradation of melanosomes and inhibits the formation of the membranous structures within the cell that transport pigment. By disrupting both the chemical synthesis and the physical transport of melanin, Hydroquinone effectively reduces the amount of pigment that reaches the skin's surface.
| Parameter | Value |
|---|---|
| Bioavailability | 35% - 45% (Topical absorption) |
| Protein Binding | Data Limited |
| Half-life | ~2-3 hours (Systemic) |
| Tmax | ~1-2 hours (Peak plasma levels after application) |
| Metabolism | Hepatic (Glucuronide and Sulfate conjugation) |
| Excretion | Renal (>90% as metabolites) |
Hydroquinone is the primary member of the Melanin Synthesis Inhibitor [EPC] class. It is chemically related to other phenols but is unique in its specific affinity for the tyrosinase enzyme. Related compounds include Arbutin (a naturally occurring derivative) and Monobenzone (which causes permanent, irreversible depigmentation and is used only for vitiligo).
Common questions about Obagi C Rx System C Clarifying Serum
Hydroquinone is a medical-grade skin-lightening agent used to treat various forms of hyperpigmentation, which is the darkening of certain areas of the skin. It is most commonly prescribed for melasma, a condition often caused by hormonal changes that results in symmetrical brown patches on the face. Additionally, it is highly effective for fading age spots (solar lentigines), freckles, and the dark marks left behind after acne or skin injuries (post-inflammatory hyperpigmentation). The drug works by blocking the enzyme tyrosinase, which is essential for the production of melanin, the pigment that gives skin its color. It is important to use this medication only under the supervision of a healthcare provider to ensure the correct diagnosis of your skin condition.
The most common side effects associated with Hydroquinone are localized to the area where the cream is applied and include mild stinging, burning, redness, and dryness. Many patients notice a slight 'peeling' effect as the skin begins to renew itself and the pigmented cells are shed. These reactions are typically mild and often subside as the skin builds tolerance to the medication over the first few weeks. However, if you experience intense itching, crusting, or the formation of small blisters, you should stop using the product and contact your doctor. It is also common to experience increased sensitivity to the sun, making regular sunscreen use mandatory during treatment.
There is no known direct chemical interaction between topically applied Hydroquinone and the consumption of alcohol. Because Hydroquinone is applied to the skin and only a portion reaches the bloodstream, it does not interact with alcohol in the same way that many oral medications do. However, alcohol is a known vasodilator, meaning it can cause the blood vessels in your face to expand, leading to flushing or increased redness. If your skin is already irritated or red from the Hydroquinone treatment, drinking alcohol might temporarily worsen this appearance. For the best results in skin health, it is always advisable to consume alcohol in moderation while undergoing any dermatological treatment.
Hydroquinone is generally not recommended for use during pregnancy. It is classified as FDA Pregnancy Category C, meaning that animal studies have shown potential risks or there is a lack of sufficient human data. A significant concern with Hydroquinone is that about 35% to 45% of the topical dose is absorbed into the mother's bloodstream, which is a much higher absorption rate than many other topical medications. Since melasma (often called the 'mask of pregnancy') is driven by hormones and frequently fades on its own after delivery, most doctors advise waiting until after pregnancy to begin treatment. If you are pregnant or planning to become pregnant, you should discuss safer alternatives with your healthcare provider.
Patience is essential when using Hydroquinone, as it does not provide overnight results. Most patients begin to see a visible lightening of their dark spots after about 4 to 8 weeks of consistent, twice-daily application. This timeframe is necessary because Hydroquinone only prevents the production of *new* pigment; it does not 'bleach' the pigment that is already in your skin cells. You must wait for your current, pigmented skin cells to naturally shed and be replaced by the new, lighter cells being produced underneath. If you do not see any improvement after 2 to 3 months of regular use, you should consult your dermatologist, as the pigment may be too deep for a topical cream to reach.
Yes, you can stop using Hydroquinone suddenly without experiencing physical withdrawal symptoms, as it is not an addictive substance. However, stopping the medication without a proper maintenance plan can lead to 'rebound hyperpigmentation,' where the dark spots return, sometimes even darker than before. This happens because the tyrosinase enzyme is no longer being inhibited and will begin producing melanin again, especially if the skin is exposed to the sun. Most dermatologists recommend a 'tapering' approach or switching to a non-prescription brightening agent like azelaic acid or kojic acid to maintain the results. Always continue using high-SPF sunscreen even after you stop using Hydroquinone.
If you miss a dose of Hydroquinone, apply it as soon as you remember to maintain the consistency of the enzyme inhibition. However, if it is nearly time for your next scheduled application, it is better to skip the missed dose entirely and simply continue with your regular routine. You should never apply a double amount of the cream or use it more frequently than prescribed to 'catch up.' Applying too much Hydroquinone can cause severe skin irritation, chemical burns, and increases the risk of systemic absorption. Consistency is more important than the exact timing of a single dose, so focus on returning to your twice-daily schedule as soon as possible.
No, topical Hydroquinone does not cause weight gain. Weight gain is a common side effect of oral corticosteroids or certain hormonal medications, but Hydroquinone is a melanin synthesis inhibitor used only on the skin. Even though a portion of the drug is absorbed into the systemic circulation, it does not affect the metabolic processes, appetite, or water retention mechanisms that lead to weight changes. If you are using a combination product that contains a corticosteroid (like Tri-Luma), the amount of steroid absorbed through the skin is generally too low to cause systemic weight gain unless used excessively over very large areas of the body for a very long time.
Hydroquinone can be used alongside many other medications, but you must be careful with other topical skin products. You should specifically avoid using Hydroquinone at the same time as products containing benzoyl peroxide or hydrogen peroxide, as this can cause a temporary orange or brown staining of the skin. It is frequently used in combination with retinoids (like Tretinoin) and mild steroids, but this should only be done under medical supervision to prevent severe skin irritation. Always inform your doctor about all the medications you use, including herbal supplements like St. John's Wort, which can increase your skin's sensitivity to the sun while using Hydroquinone.
Yes, Hydroquinone is widely available as a generic medication in both 2% and 4% concentrations. Generic versions are therapeutically equivalent to brand-name products (such as Lustra or Melquin) and are generally more cost-effective for patients. In the United States, following the 2020 CARES Act, both generic and brand-name Hydroquinone products require a prescription from a licensed healthcare provider. When filling your prescription, you may find it available in various 'vehicles' such as creams, gels, or solutions. Regardless of whether you use a brand-name or generic version, the active ingredient and the safety precautions, such as mandatory sun protection, remain exactly the same.
Other drugs with the same active ingredient (Hydroquinone)