Most common reasons for metal accumulation
The most common reason is water. Of course hair also absorbs air pollutants, but through water hair absorbs such metals copper, iron, calcium, magnesium and chlorine. Over time metal water pipes wear off and from one wash to another it leads to metal residue accumulation in the hair. Well water can contain even more metals. 

Different ways metal accumulation can appear in hair
We often think that metal deposits can only appear in colored or lightened hair, but it can also accumulate in natural, not colored hair. The amount of accumulated metals is also effected by hair condition and porosity. As a rule of thumb, you could say that the more porous the hair, the more metal accumulates in it. Also, fine hair usually absorbs more metals. Hair with metal build-up can feel rough and smell metallic or musty. This can easily be noticed when blow-drying. Hair also tangles more easily. In blonde hair, an unnatural yellow or green tones are usually sure signs of metal accumulation. In dark-colored hair, the hair color usually becomes more muddy and it loses shine. Red and copper-toned hair, on the other hand, quickly lose brightness. 

Effects of metal accumulation on hair and hair coloring process
Metal deposits must be removed from the hair, because over a longer period of time the deposits damage the hair, leaving it prone to breakage. Metals also create challenges to coloring process. Metals react during color and lightening treatments, which can cause uneven coloring results, the end result of the color can be completely different from what you wanted, or in the worst case, hair can even break during the treatment.

Deep cleansing shampoo does not necessarily remove metals 
Not all deep-cleansing shampoos remove metal deposits from the hair, but there are specialised  products for metal removal. Perfume free DS product range includes products that remove metal deposits as well as deep cleanse the hair and scalp.

Also styling products create build-up in hair and scalp  
Sebum and residues of styling products accumulate in the hair and scalp. Products used especially in the root area, such as dry shampoo, stress not only the hair but also the scalp. If the hair and scalp are not cleaned with a deep-cleansing shampoo, the accumulated dirt slows down or even prevents a healthy hair growth. Impurities can cause irritation and itching of the scalp.

Regular deep cleanse 
The need for deep cleaning heavily depends on the hair type and condition, as well as how much metal accumulates in the hair and how much styling product is used in the hair. If styling products are used in high amounts or the water contains metals, deep cleaning is recommended once a week. Otherwise, deep cleaning should be done every 2–3 weeks.   

Benefits of metal removal and deep cleaning 
High-quality deep-cleansing and metal-removing products do not stress or strip the hair, but rather the opposite. After the treatment, the hair feels silky soft and elastic, it looks brighter, doesn't tangle as easily and becomes beautifully shiny.