We often say that SMP differs from a traditional tattoo because we place pigment at a shallower depth than normal tattooists. There are other differences, notably around technique and types of needle used. This is covered in our earlier piece on why we prefer not to say ‘hair tattoo’.
As most people know, skin is our largest and most visible organ, covering nearly 2m² and making up almost a sixth of our body weight. It consists of three main layers – the epidermis, the dermis and the subcutis – each of which is made up of several sub-layers.
Keeping it simple and shallow
We usually simplify the issue of depth by stating that the pigment goes just below the epidermis. To expand on this the diagrams on this page will undoubtedly help. In Scalp Micropigmentation the needle deposits pigment in the uppermost layer of the dermis. This is known as the papillary layer. The papillary contains a thin arrangement of collagen fibres and supplies nutrients to select layers of the epidermis. It also regulates temperature.
Skin is a living, evolving organ. The epidermis replaces itself about every 30-45 days. The thickness of the epidermis on the scalp is only about 60-100 microns thick, ironically about the same as a human hair or 80gsm piece of paper – this is 0.06-0.10mm.
Right and wrong, why depth is important
We often talk about the difference between experienced practitioners and newbies or novices, how the latter can frequently mess-up a procedure by going too shallow or too deep. The technical explanation for this is that if the needle penetrates to the mid-dermis or deeper into the hypodermis (the fat layer), it creates a blurred impression or a blow-out. When healed this means that you will not have a clear, accurately sized dot or reproduction of hair, but a vague impression which is much too large. As the epidermis is in a regular cycle of regeneration if the practitioner goes too shallow the pigment will simply disappear over time, no pigment will last in this layer.
The pigment itself is also an important part of the process. The correct pigments are designed to be retained in the upper layer of the dermis. The pigment particles become engulfed or overwhelmed by dermal cells and macrophages. The particles of pigment then live suspended in the upper layer of the dermis. This is the only way pigment particles can remain visible, by remaining in this state of suspension. Cells can die with pigment particles in them, some get taken away by the lymphatic system and others get swallowed again and re-suspended in the upper layer of the dermis. In some cases of alopecia, due to the nature of the condition, the pigment is attacked more aggressively and pigment is absorbed. This is one of the main reasons alopecia requires a slower treatment and an increased number of sessions.
Keeping the pigment in suspense
To summarise, the epidermis consists of five layers. Any pigment placed in the epidermal layer will shed. The dermis consists of two layers, the reticular which comprises of about two thirds of the dermis. Sitting on the reticular is the papillary dermis which makes up the third. Traditional tattooists generally penetrate to the level of the reticular or upper reticular. SMP practitioners should penetrate the papillary.
As both Male Pattern and Female Pattern baldness progresses, both the epidermis and dermis thins. This is partly due to the ageing process but also to the loss of hair structures in the dermis. According to some studies, females have a thicker dermis than males. Regardless of the thickness of skin, the pigment stays suspended in the upper layer of the dermis. It must be suspended in dermal cells to last for years.
Sources of information and further reading
- Skin structure and function
- Anatomy of the skin
- Standardization of SMP procedure and its impact on outcome, Journal of Cutaneous and Aesthetic Surgery
- Tattoo ink, where does it all go?
With thanks to Karen Chung Nicolaou, Carl Barton, Kate Dawes, Valerie Weber, Mariannthy Nicolaou and Team Micro International for sparking the debate.