A tumor suppressor protein, also known as the "Guardian of the Genome". It plays an important role in cell cycle control and apoptosis (the death of cell). Defective p53 could allow abnormal cells to proliferate, resulting in cancer. In normal cells, the p53 protein level is low. High level of p53 may also accelerate the aging process by excessive apoptosis.

A minute quantity or fragment, a tiny piece of matter.

Smaller than the atom. Proton, neutrons and electrons are the three main subatomic particles found in an atom.

Any agent capable of causing disease (from Greek word pathos meaning "suffering, passion", and gignomai meaning "give birth to").

PDT stands for PhotoDynamic Therapy, which is a medical treatment that uses a photosensitizing drug (a drug that becomes activated by light exposure) and a light source to activate the applied drug. PDT therapy is currently used in a number of medical fields including oncology, dermatology and cosmetic surgery.

Organic compound composed of a series of amino acids linked by chemical bonds (peptide bonds). Peptides are named after the Greek word peptos, meaning “digestible”.

A pH (potential of Hydrogen) measurement reveals if a solution is acidic or alkaline (also base or basic). If the solution has an equal amount of acidic and alkaline molecules, the pH is considered neutral. Very soft water is commonly acidic, while very hard water is commonly alkaline. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic.

The luminescence of a substance when it is excited by light. The process of phosphorescence occurs in a manner similar to fluorescence, as they both involve absorption of energy, but with a much longer excited state lifetime. "Glow-in-the-dark" light (phosphorescence) is not as bright as fluorescence but lasts much longer.

The process of activating a substance by means of radiant energy and especially light.

Sensitivity to light that causes allergic reactions.

Photocatalysis comes from the Greek words photo meaning light and catalysis, which is the process of a substance (the so called catalyst) accelerating chemical reactions without itself being altered or consumed. Photocatalysts mediate chemical reactions and are activated by light energy.

Any chemical reaction caused by absorption of light (including visible, ultraviolet, and infrared). The light excites atoms and molecules (shifts some of their electrons to a higher energy level) thus making them more reactive.

The branch of Chemistry that deals with the chemical reactions initiated by light. A molecule changes photochemically only if it absorbs a photon, or received energy from another molecule that absorbed a photon already. The energy needed for the chemical reaction is provided by photons.

A molecule that can change its atomic structure and therefore its properties, when exposed to electromagnetic radiation.

The phenomenon of reversible transformation of molecules between two structural forms with different absorption spectra. Photochromism is practically observed as the process of inducing color changes in a medium using light (i.e. electromagnetic radiation).

Phenomenon in which electrically charged particles are released from or within a material when it absorbs electromagnetic radiation. The effect is often defined as the ejection of electrons from a metal plate when light falls on it.

An electron released in photoemission, i.e. due to the  interaction with electromagnetic radiation.

The ejection of electrons from matter following the absorption of one or more photons.

A very small quantity (quantum) of electromagnetic radiation containing a discrete amount of energy. Photon may be also considered as a particle of light.

The physics of light, especially of its interaction with matter.

The process in which light energy is converted into chemical energy in the form of carbohydrates.

Adverse reaction to ultraviolet light or sunlight caused by chemicals, such as the furanocoumarins.

A non mechanical device (in particular, a specialized semiconductor diode) usually made of silicon alloys that convert sunlight directly into electricity.

The basic physical process through which a photovoltaic cell (PV cell) converts sunlight into electricity. When photons of sunlight strike a PV cell they may be reflected, absorbed, or pass through the cell. The absorbed photons may generate electricity through the emission or ejection of electrons from the surface of the cell, in response to the light. The term photovoltaic comes from the Greek words “photo” (light) and “voltaic”, which refers to electricity.

The branch of Chemistry that studies chemical processes from the point of view of Physics.

One trillionth (10-12) of a second.

It is sometimes regarded as the fourth state of matter (the first three being solid, liquid, and gas) mainly consisting of nuclei and electrons. More than 99% of the matter in the universe may exist in the plasma state.

A substance that pollutes, especially a waste material that contaminates air, soil, or water.

A material constructed of smaller molecules of the same substance that are chemically bonded to form larger molecules (from a Greek word meaning "many parts").

The study of the synthesis, structure and properties of polymers.

A widely used plastic; it is a polymer of styrene. Polystyrene is a colorless, transparent thermoplastic that is produced either as a solid or as a foamed plastic (commonly marketed under the trade name Styrofoam). Its many uses include electrical and thermal insulation, translucent window panels, storage-battery cases, and toilet articles.

Porphyrins are biological pigments (i.e. substances that impart color to materials) found in both, animal and plant cells. Their name comes from a Greek word reffering to the purple colour.

Any identifiable substance that is used to detect, isolate, or identify another substance.

A molecule deliberately added to a system which changes a property, for example fluorescence, in response to a stimulus, which may be biological or chemical (e.g. the presence of a pollutant).

A substance that forms as a result of a chemical reaction.

A biological macromolecule made of 20 basic building blocks  called amino acids. Proteins are named after the Greek word protos, meaning “primary” or “first rank of importance”.

The physical process by which a protein folds into its characteristic three-dimensional structure.

The process in which cells build proteins. The “central dogma” of molecular biology as articulated by the British molecular biologist Francis Crick, put it simply as: “DNA makes RNA makes protein, proteins make us.”

A particle with a positive charge commonly found in the nucleus of atoms.

Psoriasis is a chronic autoimmune disease that appears on the skin. It occurs when the immune system sends out faulty signals that speed up the growth cycle of skin cells.

A therapy used for skin diseases such as severe psoriasis, atopic dermatitis, vitiligo, vesicular eczema etc. PUVA stands for psoralen (P) and ultraviolet A light (UVA), a therapy in which the patient is exposed first to psoralens (drugs containing chemicals that react with ultraviolet light) and then to UVA light.