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A
[EN] Acide
Acid
Substance with a pH less than 7. Opposite to "alkaline" or "basic".
Alkaline
Said of a substance which has the properties of a "base", i.e. having a pH greater than 7. Synonymous with "basic", as opposed to "acid".
[EN] Acide aminé
Alopecia
Progressive loss of hair or fur, partial or generalised. Alopecia may end in baldness.
[EN] Acide gras
Amino-acid
Small molecule of 10 to 15 atoms, the basic component of the proteins of all living things. 20 in number, they join together in chains to form the protein. As an illustration they might be compared with the letters of the alphabet which are the building blocks of our writing system.
[EN] Alcalin
Anagen (phase)
Growth phase in the hair growth cycle. On average it lasts for 3 years.
[EN] Alopécie
Androgens (phase)
Male hormones which in particular regulate the appearance and the development of the male sexual characteristics (e.g. testosterone)
[EN] Anagène (phase)
[EN] Androgènes
B
Baldness
Complete or partial absence of hair. Baldness is the ultimate form of alopecia
[EN] Base
[EN] Biomimétique
Base
Substance with a pH greater than 7 (e.g. ammonia)
Biopsy
Removal from a living being of a fragment of tissue for testing/sampling.
Biomimetic
Said of the scientific approach which consists of synthesising a substance by imitating the living process which naturally produces it.
Biopsy
Sample from a living being of a fragment of tissue for microscopic examination.
C
[EN] Canitie
Canities (Latin)
State of hair having become white by progressive depigmentation.
[EN] Catagène (phase)
Catagen (phase)
Regression phase in the hair growth cycle. On average it lasts for 3 weeks.
[EN] Calvitie
Caucasian
Term used by anthropologists to group together Indo-European human groups, and more generally white skin groups.
[EN] Caucasien
Ceramide
Particular class of lipids naturally present in the skin and hair.
Connective tissue
Tissue which has the role of supporting the other tissues (or organs of the body) and protecting, nourishing and holding them together.
[EN] Cellule souche (ou pluripotente)
[EN] Céramide
Cortex
Main part of the hair fibre, protected by the cuticle
Cortical
Relating to the cortex.
[EN] Ciment intercellulaire
[EN] Conjonctif (tissu)
Cuticle
External part of the hair fibre.
[EN] Cortex
Cysteine
Sulphur containing amino-acid, a constituent of proteins.
[EN] Cortical
[EN] Cuticule
[EN] Cystéine
D
Dermal papilla
Component arising from the dermis which is the "motor" of the hair follicle.
[EN] DERME
Dermis
Deep layer of the skin, covered by the epidermis and formed from connective tissue.
[EN] Desquamation
[EN] Duvet
Desquamation
Elimination of superficial layers of the epidermis in the form of small flakes.
Disulphide bridge
Type of chemical bond involving two sulphur atoms. It is a strong bond. In hair the disulphide bridges involve cystine, an amino acid formed from the joining of two cysteine molecules.
E
Effluvium post-partum
Sudden and excessive loss of hair which occurs in women in the months following giving birth.
[EN] Effluvium post-partum
[EN] Elasticité
Elasticity
Property of certain bodies of returning to their original shape and volume when the force exerted on them ceases to act.
[EN] Enzyme
Epidemiology
Study of the relationship between diseases or any other biological phenomenon and various factors (life-style, surroundings or social environment, particular individual features) likely to exert an influence on their frequency, distribution, and development.
[EN] Epidémiologie
[EN] Epiderme
Epidermis
Superficial layer of the skin, covering the dermis and formed from epithelial tissue.
[EN] Epithélial
Epithelial
Concerning the epithelium.
[EN] Epithélium
Epithelium
Tissue formed from one or more layers of cells which covers the body (epidermis), the internal cavities (mucosae) or which makes up the glands.
Eumélanine
Eumelanin
[EN] Eumélanine
F
Fatty acid
Organic acid, a major constituent of lipids. A fatty acid has a long hydrocarbon chain and a terminal carboxyl group
G
Genetic heritage
All of the genetic material carried by an individual and representing his hereditary make-up, fixed at the time of fertilisation
H
Hair follicle
Invisible part of the hair buried 4 mm under the scalp and which is the place where the hair is produced.
Henna
Plant from the Middle-East and North Africa. Dried and ground henna leaves produce a powder used to dye hair and nails.
Homeostasis
Stabilisation in living organisms of various biological parameters.
Hormone
Chemical substance produced by a group of cells or by an organ, released directly into the blood, and exercising a specific biological action on the functioning of an organ or numerous physiological processes such as growth, metabolism or reproduction.
Hydrogen bond
Type of chemical bond forming between a hydrogen atom and electronegative atoms such as oxygen, nitrogen and fluorine. By nature it is a weak bond
Hydrophobic bond
(or Van der Waals force) Type of electrostatic bond, which forms between two polarised molecules (electrostatically charged). It is a weak bond.
I
Intercellular cement
Extra-cellular substance which ensures the cohesion of cells within a tissue.
In vitro
(Latin words: "in glass") Used to describe any biological experiment carried out outside of the organism. As opposed to in vivo.
In vivo
(Latin words: "in the living") Used to describe any biological experiment carried out within the living organism. As opposed to in vitro.
K
Keratin
Sulphur rich fibrous protein, insoluble in water and very strong. It forms the essential part of hair fibre, the skin, nails, horns, hooves, feathers and wool. It is also present in the superficial cells of the epidermis.
Keratinocyte
Cells of the epidermis or of hair follicles, responsible for the synthesis of keratin.
L
Lipids
Fatty chemical substances, found in all living organisms, playing a considerable role in cell structure and with an important energetic role as well.
M
Marker
Chemical element introduced into a product or tissue which allows it to be monitored and its evolution seen.
Melanin
Coloured pigment giving colour to the hair and skin.
Melanocyte
Cells of the epidermis or of hair follicles, responsible for the synthesis of melanin and transmitting it to the keratinocytes.
Micrometre
Unit of measurement equal to one millionth of a metre or a thousandth of a millimetre (formerly: micron).
Micron
Former name of the micrometre ("micrometre" officially replaced "micron" in 1967).
Mitosis
Usual method of cell multiplication in which a mother cell divides into two identical daughter cells, each containing a set of chromosomes identical to those of the mother cell.
N
Neomorphogenesis
Morphogenesis being the process which results in the specialisation of cells and the production of an organ, neomorphogenesis is the renewal of this process.
O
Oestrogens
Female hormones secreted by the ovaries and which in particular control the phase of ovulation. (e.g. oestradiol).
Oxidation
Combination of a substance with oxygen and, more generally, a reaction in which an atom loses electrons. The opposite inseparable reaction is called reduction.
P
Papille dermique
Composant issu du derme et "moteur" du follicule pileux.
pH
(Abbreviation of "hydrogen potential".) Index expressing the activity (or concentration) of hydrogen ions in a solution. If the pH is less than 7, the solution is acidic. If it is equal to 7, it is neutral. If it is greater than 7, it is alkaline.
Phaeomelanin
Melanin pigment ranging in colour from yellow to red.
Photomicrograph
Technique for the evaluation of the state of a head of hair which consists of shaving 1 cm² of the scalp, then photographing this zone just after shaving and again 2 days later.
Plasticity
Property of certain bodies to deform under the influence of an external force and keep this new form when the force ceases to act.
Precursor
Molecule which can be transformed into a biologically active product. A colour precursor is a natural or synthetic uncoloured substance the transformation of which leads to the production of melanin or colorant.
Protein
Macromolecule formed from the association of from 4 to several thousand amino acids. They are essential components of cells (the word "protein" comes from the Greek protos which signifies "first").
R
Reduction
Reaction in which part of the oxygen is removed from a substance and, more generally, a reaction in which an atom gains electrons. The opposite inseparable reaction is called oxidation.
S
Sebocyte
Cell of the sebaceous glands responsible for the synthesis of sebum.
Sebum
Greasy material produced by the sebaceous glands associated with the hair follicles and which naturally lubricates the hair.
Spectroscopy
Study of the spread of energy of electromagnetic radiation and particles emitted by an excited nucleus.
Squalene
Lipid specifically forming part of the composition of sebum.
Stem cell (or cell capable of differentiating)
Non-specialised cell capable of giving rise to different specialised cells.
Sterol
Widespread alcohols in the animal and plant kingdom. Cholesterol, vitamin D and the steroids come into this group.
Synchrotron
Particle accelerator in which the magnetic field increases with the speed of the particles.
Synthesis
Production of a chemical compound from its component elements or from compounds with a simpler formula.
Synthetic
Produced artificially by chemical synthesis.
T
Telogen (phase)
Phase of loss of the hair in the hair growth cycle. On average it lasts for 3 months.
Testosterone
Male hormone secreted by the testicles and affecting the development of the genital organs and male secondary sexual characteristics.
Thermoregulation
Regulatory mechanism by which the internal temperature of the body of mammals and birds is maintained constant.
Triboelectricity
Static electricity produced by friction.
Trichotillomania
Compulsive frequent hair pulling or twisting which may go as far as pulling the hair out.
Triglyceride
Variety of lipid playing a role in energy storage in animal and plant cells.
Tyrosinase
Enzyme activating the oxidation of tyrosine, resulting in the production of melanin.
Tyrosine
Amino-acid playing an important role through the organic compounds derived from it (melanin, adrenaline, iodated compounds from the thyroid gland).
V
Vellus hair
All of the miniature hairs which grow on the human body. The downy hair which remains in areas of alopecia is the result of miniaturisation of the hair follicle
Vertex
Top of the head.
Video-microscope
System of microscopy associating a video camera with an objective magnifying between 10 and 1000 times, and allowing continuous observation and recording of pictures.
Videotrichogram
Technique for evaluation of the state of a head of hair derived from the phototrichogram technique: which consists of shaving 1 cm2 of the scalp, then filming this area just after shaving then at regular intervals.
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