Electroencephalography (EEG) is a medical test that non-invasively measures the electrical activity of the brain. The procedure relies on placing small metal sensors, called electrodes, directly onto the scalp to detect tiny voltage fluctuations generated by firing brain cells. Capturing these minute signals requires an extremely stable and electrically conductive connection between the electrode and the skin. Hair and the natural scalp barrier create a physical challenge that must be carefully managed to ensure accurate brain wave data.
The Scalp Interface and Signal Impedance
The primary technical challenge hair presents to an EEG is increased signal impedance, which is the opposition to the flow of electrical current. For an accurate reading, resistance at the skin-electrode interface must be minimized, typically targeting values below five kilo-Ohms. The outermost layer of the skin, the stratum corneum, is composed of dead, keratinized cells that act as a natural insulator, significantly contributing to high impedance.
Hair strands complicate signal acquisition by physically pushing the electrode away from the scalp surface, creating microscopic air gaps. Since air is a poor electrical conductor, these air pockets drastically increase impedance, weakening the brain signal before it can be measured. Hair shafts are also composed of non-conductive keratin, adding another layer of resistance. This interference necessitates using a specialized conductive medium to electrically bridge the gap between the electrode and the active skin layer.
The volume and texture of hair affect the impedance encountered. For individuals with coarse or tightly coiled hair, the density and structure make achieving a low-impedance connection more difficult. Standard electrodes placed on curly hair can register impedance values far exceeding acceptable limits, sometimes reaching hundreds of kilo-Ohms. Preparation steps are specifically designed to overcome the insulating properties of the skin barrier and the hair itself.
Patient Preparation and Electrode Application
Successful EEG recording begins with patient preparation, focusing on hair hygiene before arrival. Patients are instructed to wash their hair thoroughly the night before or the morning of the procedure using only shampoo. The hair must be clean, completely dry, and free of any styling products, including conditioners, oils, gels, or hair sprays. These cosmetic products leave a non-conductive residue on the scalp and hair, creating electrical resistance that elevates impedance.
A technician begins the application process by measuring the head to determine the exact locations for electrode placement. This is done using the International 10-20 system, a standardized method that ensures electrodes are positioned over specific brain regions. The system uses anatomical landmarks, such as the nasion (bridge of the nose) and the inion (prominent bump at the back of the skull), to proportionally measure and mark the sites.
After marking the locations, the technician prepares the scalp surface to reduce the electrical barrier of the stratum corneum. A small amount of a mild abrasive gel or paste is gently rubbed onto the skin at each marked site using a blunt-tipped swab. This gentle exfoliation removes superficial dead skin cells, effectively lowering impedance and improving electrical conductivity. The technician then applies a thick, conductive paste or gel, such as Ten20 or Elefix, into the cup of the electrode before pressing it firmly onto the prepared spot.
This conductive medium displaces residual air and establishes a stable electrical pathway from the scalp to the metal sensor. For longer-term monitoring, a stronger medical adhesive, such as collodion glue, may be used to secure the electrodes firmly for several days. The patient must remain still during application and recording to prevent the electrodes from shifting, which could introduce movement artifacts or cause a loss of the electrical connection.
Post-Procedure Care and Residue Removal
After the EEG recording is complete, the electrodes and conductive material must be removed, which is often a concern for patients. The ease of removal depends on the type of conductive medium used. Water-soluble pastes, frequently used for routine, shorter EEGs, are simple to remove and typically wash out completely with one or two applications of regular shampoo.
Stronger adhesives like collodion glue, used for long-term or ambulatory EEGs, present a substantial cleanup challenge because they are water-resistant. The technician first uses a specific solvent, such as acetone or a commercial collodion remover, to dissolve the glue and detach the electrodes. Despite this initial step, patients often have hardened, tacky clumps of residue remaining in their hair.
For at-home removal of remaining collodion, skin-safe oils are recommended to help break down the adhesive bond. Massaging oil into the dry, affected areas and allowing it to soak can significantly loosen the residue. Following the oil treatment, a clarifying shampoo or mild dish soap can be used to wash out the oil and dissolved glue. Complete removal sometimes requires multiple washes and gentle combing to extract all clumps from the hair strands.