The 'Stacks' parameter dictates the number of times the laser fires energy into the exact same microscopic treatment zone before the scanner moves to the next point.
Instead of distributing energy across a wider surface area, increasing the Stacks setting concentrates repeated pulses on a single spot. This allows the laser to bypass the surface barrier effectively and drive thermal energy vertically into the deeper layers of the dermis.
The Core Takeaway The Stacks setting is primarily a tool for controlling vertical penetration depth. By applying energy multiple times to the same site, you can break down tough, fibrotic tissue in the deep dermis—such as older stretch marks—without necessarily increasing the width of the surface injury.
The Mechanics of Vertical Penetration
Overcoming Tissue Resistance
The skin acts as a barrier that resists energy absorption. A single pulse of laser energy may only penetrate the superficial layers of the epidermis or upper dermis.
By utilizing the Stacks parameter, the laser "drills" down into the tissue. The first pulse ablates the surface, clearing a path for subsequent pulses to reach deeper structures that a single pulse could not access.
Targeting Deep Dermal Layers
The primary goal of this vertical depth is to reach the reticular dermis.
This is where the majority of structural collagen resides. Delivering thermal damage to this specific depth is necessary to trigger the body's wound-healing response, resulting in significant collagen regeneration and remodeling.
Clinical Application: Treating Fibrosis
Breaking Down Striae Distensae
The Stacks parameter is particularly critical when treating Striae Distensae (stretch marks), specifically the older, white variety known as Striae Alba.
These lesions are characterized by dense, fibrotic scar tissue that is resistant to remodeling. Shallow treatments often fail to produce visible results on this tissue type.
Structural Remodeling
To treat these older scars effectively, the laser must disrupt the fibrotic bands located deep within the skin.
Increasing the Stacks ensures the energy bypasses the healthy or less damaged surface skin to deposit heat directly into the scar tissue. This stimulates the production of new, organized collagen to replace the disorganized fibrotic fibers.
Understanding the Trade-offs
The Risk of Excessive Thermal Bulk
While Stacks increase depth, they also increase the total amount of heat (thermal load) delivered to a specific column of tissue.
If the Stacks are set too high without adjusting other parameters, you risk "bulk heating." This occurs when the heat spreads laterally into the surrounding healthy tissue, rather than remaining confined to the microscopic treatment zone.
Balancing Efficacy and Safety
The goal of fractional laser therapy is to leave bridges of healthy skin intact to speed up healing.
Excessive stacking can bridge these gaps thermally, potentially leading to delayed healing or adverse effects like Post-Inflammatory Hyperpigmentation (PIH). The operator must balance the need for depth against the skin's ability to dissipate the accumulated heat.
Making the Right Choice for Your Goal
The Stacks parameter is not a "set and forget" dial; it must be modulated based on the specific pathology you are treating.
- If your primary focus is Superficial Resurfacing: Keep the Stacks setting low (1) to treat surface texture and pigmentation without unnecessary deep tissue injury.
- If your primary focus is Deep Scar Revision (Striae Alba): Increase the Stacks setting (2-3) to ensure energy penetrates through the fibrosis to stimulate deep collagen remodeling.
Use Stacks to convert your laser from a surface-polishing tool into a deep-tissue remodeling instrument.
Summary Table:
| Feature | Low Stacks (1) | High Stacks (2-3+) |
|---|---|---|
| Energy Focus | Superficial layers | Deep dermal layers |
| Tissue Impact | Surface polishing | Vertical 'drilling' / Remodeling |
| Primary Goal | Texture & Pigmentation | Fibrotic scar revision (Striae) |
| Thermal Load | Low (Minimal lateral heat) | High (Increased thermal bulk) |
| Healing Time | Faster | Moderate (Due to depth) |
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References
- Rehab Mohamed Sobhi, Mona Abd El Fattah Abd El Wahab. Comparative study between the efficacy of fractional micro-needle radiofrequency and fractional CO2 laser in the treatment of striae distensae. DOI: 10.1007/s10103-019-02792-7
This article is also based on technical information from Belislaser Knowledge Base .
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