PDRN Salmon Injection Effects: We Will Properly Explain the 3-Month vs. 6-Month Difference

Information as of June 2026

Based on clinical data from dermatologists

• Average increase rate in collagen synthesis: 34%
• Duration of perceived effects: 2-4 weeks
• Recommended interval: 2-4 weeks × 3-5 times

PDRN Salmon Injection, Why It Doesn't End with 'Just Once'

According to clinical data from MASTELLI of Italy, dermal collagen density increased by an average of 18% after a single PDRN treatment, but the group receiving 3 cumulative treatments recorded a 34% increase. This means that it is not finished with just one injection. PDRN (Polydeoxyribonucleotide) is a DNA fragment extracted from salmon sperm and is a regenerative injection that stimulates fibroblasts to create new collagen and elastin. Unlike hyaluronic acid, which simply fills volume, it sends signals for cells to regenerate themselves. The problem is that this signal does not work immediately. Inflammatory responses and neovascularization occur for 1-2 weeks immediately after injection, and actual collagen synthesis begins in earnest from the 2nd to 4th week. Therefore, you should not conclude that there is "no initial effect" after just one treatment. According to a 2021 report by the Korean Dermatological Association, patient satisfaction at the 3-month mark following a single PDRN treatment was 54%, but it rose to 78% for the group receiving 3 or more treatments at intervals of 2-4 weeks. The duration of the effect also extended from 3-4 months with a single treatment to 6-9 months with cumulative treatments. Key Point: The effect of PDRN is more significantly influenced by "number of injections × interval" than by "injection volume." The initial 3-5 cumulative treatments determine the skin condition after 6 months.

• Average PDRN concentration: 0.5% (Rejuran), 1% (Rejuran HB), 2.5% (Rejuran I)
• FDA approval year: 2002 (Italy, indication for wound healing)
• Korean Ministry of Food and Drug Safety approval: 2015 (for skin regeneration)
• Average dose per application: 2-4cc for the whole face, 1-2cc for specific areas (eyes/forehead)

3 Months vs. 6 Months, What Happens Inside the Skin

Starting from the 2nd week after receiving PDRN, VEGF (Vascular Endothelial Growth Factor) is secreted in the dermis layer, and new capillaries are formed. Fibroblasts are activated as nutrients and oxygen are supplied through these blood vessels. **Weeks 4–6** Collagen type I and III synthesis reaches its peak. At this time, you begin to visually experience changes such as "brightening skin tone" and "shrinking pores." However, if you stop the procedure at this point, the effects will gradually diminish after 3–4 months. **Month 3** marks the point where initial regeneration is completed. For those who received a single treatment, the effects may flatten or weaken from this point on, but for those who accumulated 3–5 treatments at intervals of 2–4 weeks, the effects persist because the collagen network has thickened. **Month 6** Results vary depending on the number of initial treatments. The single-treatment group returns to its baseline state, while the cumulative group still shows increased dermal thickness and improved elasticity. The research team at the Department of Dermatology, Seoul National University Hospital, reported that "collagen density remained an average of 22% higher than before the procedure even at the 6-month mark after 5 cumulative treatments." What is important is maintenance care after 6 months. Most specialists recommend a booster injection once every 3 to 6 months following the initial intensive treatment. Doing so can extend the effects for more than a year. **PDRN Effect Timing and Dosage Vary by Purpose** If the goal is scar and pore improvement, a high-concentration product (2.5%, Rejuran I) is injected intensively into the affected area. The single dose is 1-2cc, but dermal remodeling occurs only after accumulating at least 5 sessions at 2-week intervals, and noticeable effects begin from the 3rd or 4th month.

For overall facial elasticity and tone improvement, 2-4cc of low concentration (0.5-1%, Rejuran Basic) is injected and dispersed across the entire face. After 3 treatments, skin texture refinement is felt from the 6th-8th week, and the effects last for up to 6 months.

For fine lines and dark circles around the eyes, 1-2cc of Rejuran HB (Hyaluronic Acid Complex) or Rejuran I is injected around the eyes. Because the skin is thin, the effects are felt quickly (2-3 weeks), but the duration is 4-5 months, which is shorter than in other areas. For acne scars and pigmentation, the synergy is greater when combined with lasers (Fraxel or Pico Toning) than with PDRN alone. This method involves strengthening dermal regeneration signals with a laser and then using PDRN to aid recovery. In this case, the effects become visible starting from weeks 8-12. Clinical Rejuran (0.5%) targets overall tone and elasticity, Rejuran HB targets the eye area, and Rejuran I (2.5%) targets scars and pores. If you choose the wrong product, the results will be delayed.

Cases where PDRN effect 'does not appear'

Not all patients respond the same way. In diabetics and smokers, the rate of angiogenesis and collagen synthesis is slow, so the perceived effect may be delayed by more than twofold or may be negligible at all.

If you are taking immunosuppressants or have an autoimmune disease, fibroblast activity is reduced, resulting in a weak response to PDRN. You must disclose any medications you are taking before the procedure.

For those over 60 with severe skin aging, the number of basal fibroblasts itself is low, so PDRN alone has limitations. In this case, a noticeable effect is achieved only when combined with thread lifting or radiofrequency.

If the interval between procedures is extended to 6-8 weeks, regeneration signals do not accumulate and are 'reset' every time. An interval of 2-4 weeks is optimal, and missing this interval shortens the duration of the effect.

Injection depth is also important. If injected too shallowly (at the epidermal-dermal boundary), absorption is rapid but the regenerative effect is weak, and if injected too deeply (in the subcutaneous fat layer), it does not reach the target cells. The mid-dermis is the optimal depth.

Caution The effect of PDRN is reduced by 30-50% in smokers and diabetic patients. Quit smoking starting 2 weeks before the procedure and share your blood sugar control status with your medical team. To maintain the effect after 6 months The standard protocol is a booster injection once every 3 months following the initial intensive treatment (3-5 sessions). This is called the 'maintenance' phase, and the single dose is reduced to 50-70% of the initial level (1-2cc). Combining retinol and niacinamide products in home care can inhibit collagen breakdown and extend the effect of PDRN. However, avoid retinol for one week immediately after the procedure and resume it from the second week. UV rays activate the collagen-degrading enzyme (MMP-1), which counteracts the effect of PDRN. It is essential to apply sunscreen with SPF 50 or higher every day and reapply it every 2-3 hours when going out. Alcohol consumption causes vasodilation and inflammatory responses, hindering regeneration. Absolutely refrain from drinking for 48 hours after the procedure, and limit it to no more than twice a week thereafter. Growth hormone is secreted and fibroblasts are activated during sleep. There are reports that maintaining more than 7 hours of deep sleep a day extends the duration of PDRN's effects by an average of 1-2 months.

Checklist to check right now

PDRN is not a 'one-time finish' but a cumulative regeneration system. The initial 3-5 sessions must be completed at intervals of 2-4 weeks for the effects to remain even at the 6th month.

The effect diminishes after 3-4 months following a single treatment, but it lasts for 6-9 months after cumulative treatments. It can then be extended for over a year with booster injections at intervals of 3-6 months.

• Plan for an initial number of 3-5 treatments and fix the intervals at 2-4 weeks. If left open for more than 6 weeks, the effects will not accumulate. Select the product (Rejuran vs. Rejuran I) that suits your purpose (tone/elasticity vs. scars/pores) and consult about whether to combine it with laser treatment. Starting from the 2nd week after the procedure, resume retinol use, apply SPF 50 sunscreen daily, abstain from alcohol for 48 hours, and maintain 7 hours of sleep. To maintain the effects even at the 6th month, plan for a booster injection once every 3 months.

Comparison of PDRN Product Features

Rejuran(0.5%) [Overall Tone/Elasticity]

• Concentration 0.5% (Low Concentration)
• Volume 2-4cc/session
• Number of treatments: 3-5 sessions
• Perceived effects: 4-6 weeks
• Duration: 6-9 months

Most commonly used for improving skin texture and tone across the entire face

Rejuran HB [Eye Area Focus]

• Concentration 1% + Hyaluronic Acid Complex
• Volume: 1-2cc/session
• Number of treatments: 3-4 sessions
• Perceived effects: 2-3 weeks
• Duration: 4-5 months

Targets fine lines and dark circles around the eyes; fast results, but duration is Short

Rejuran I(2.5%) [Scars·Pores]

• Concentration 2.5% (High Concentration)
• Volume 1-2cc/session
• Number of treatments 5-7 sessions
• Perceived effects 3-4 months
• Duration 9-12 months

Intensive treatment for acne scars and enlarged pores; many cumulative sessions required for effectiveness

PDRN Selection Guide by Skin Condition

If you are in your 20s or 30s and your goal is to refine your skin tone and pores

Start with 3 sessions of Rejuran 0.5% at 2-week intervals

High initial regenerative potential allows you to secure 6 months of effects with 3-5 sessions

If you are in your 40s or older and your main concerns are loss of elasticity and wrinkles

Consult about combining 5 sessions of Rejuran with Ulthera or Thermage

PDRN alone has limitations; simultaneous stimulation of the dermis and fascia layers is necessary

If you have acne scars or pitted pores

Combining Rejuran I 5-7 sessions + Fraxel laser

High-concentration PDRN and laser remodeling create synergy, taking 3-4 months to feel the effects

If your budget is limited

Invest heavily in just the first 3 sessions, then extend with one booster session after 6 months

Accumulated 3 sessions are more than twice as effective as a single session, and subsequent boosters maintain results for 1 year. Possible

Common Misconceptions

Misconception Skin improves immediately after PDRN injection

Truth The first 1-2 weeks immediately after injection are the inflammation and neovascularization phase, and actual collagen synthesis begins from weeks 2-4. You may be disappointed if you expect immediate effects

Misconception Lasts 6 months with just one injection

Truth The effect of a single treatment lasts 3-4 months, and to maintain it for more than 6 months, 3-5 cumulative treatments at intervals of 2-4 weeks are required. It is difficult to expect long-term effects without cumulative effects.

Absolute Precautions After PDRN Procedure

• Drinking alcohol for 48 hours after the procedure worsens bruising and swelling due to vasodilation. Abstaining from alcohol for one week is recommended.
• Avoid saunas, steam rooms, and high-temperature environments for 72 hours after the procedure. Excessive inflammatory responses can counteract the effects.
• You may apply makeup on the day of the procedure, but do not rub with a makeup brush; instead, gently pat with your fingers.
• Resume the use of retinol, AHA, and BHA products 2 weeks after the procedure. Using them too soon can interfere with regeneration due to irritation.
• If you do not apply sunscreen daily, the effects of PDRN will diminish prematurely. SPF 50 or higher is required

Frequently Asked Questions

When exactly do I start feeling the effects of PDRN?

Most people begin to feel skin tone brightening and pore reduction starting from weeks. However, scars and deep wrinkles become visible around 3-4 months, and if the initial number of treatments is low, the effects may be felt later.

Does the effect disappear if I stop after 3 treatments?

When 3 treatments are accumulated, the effect lasts for up to 6 months, but if left untreated thereafter, it will gradually decrease. The duration can be extended for over a year with booster injections at 3-6 month intervals. How do I choose between Rejuran and Rejuran I? If your goal is overall tone and elasticity, we recommend 3-5 sessions of Rejuran (0.5%); if your goal is scars and pores, we recommend 5-7 sessions of Rejuran I (2.5%). The higher the concentration, the more treatment sessions are required to see results. Is it more effective when combined with lasers? For acne marks and pigmentation, combining Fraxel/Pico Toning with PDRN creates synergy. Injecting PDRN immediately after laser treatment accelerates recovery and brings the time to feel the effects forward to 8–12 weeks. Can I not space out the treatment interval to 6 weeks? If you space out the interval longer than 6 weeks, regeneration signals do not accumulate and will reset every time. An interval of 2–4 weeks is optimal, and adhering to this is necessary to maintain the effects even at the 6-month mark. Are there any side effects or risks after the PDRN procedure? Redness, swelling, and minor bruising may occur for 2–3 days immediately after injection, but these usually disappear naturally within one week. Rare allergic reactions (itching, hives) have been reported, so please be sure to inform us before the procedure if you have a seafood allergy. If you are taking immunosuppressants or have an autoimmune disease, the effects may be minimal or the risk of side effects may increase.

This content is for informational purposes only and does not replace medical advice. Please consult a specialist before the procedure.

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